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Increases your RAM
by 256K Bytes
1764 RAM EXPANSION
Commodore Business Machines, Inc. Commodore Business Machines. Limned
1200 Wilsun Diive »Wesl Chester, PA 1938(1 3470 Pharmacy Avenue • Agincourl, Ontario. M1W 3G3
PRINTED »N USA.
Commodore" 1764 RAM
Copyright 1986 by Commodore Electronics Limited.
All rights reserved.
This software product is copyrighted and all rights reserved by Commodore Electronics,
Ltd. The distribution and sale of this product are intended for the use of the original
purchaser only. Lawful users of this program are hereby licensed only to read the program,
from its medium into memory of a computer, solely for the purpose of executing the
program. Duplicating, copying, selling, or otherwise distributing this product is a violation
of the law.
This manual is copyrighted and all rights are reserved. This document may not. in whole or
in part, be copied, photocopied, reproduced, translated or reduced to any electronic
medium or machine readable form without prior consent, in writing, from Commodore
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EITHER EXPRESSED OR IMPLIED, WITH RESPECT TO THE PROGRAM DESCRIBED
HEREIN. ITS QUALITY. PERFORMANCE. MERCHANTABILITY. OR FITNESS FOR ANY
PARTICULAR PURPOSE. THIS PROGRAM IS SOLD "AS IS". THE ENTIRE RISK AS TO ITS
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Commodore® is a registered trademark of Commodore Electronics Limited.
Commodore 64® is a registered trademark of Commodore Electronics Limited.
GEOS™ is a trademark of Berkeley Softworks.
$3G00-$33FF. The data should be the same in all these locations,
indicating the RAM expander read from the proper locations.
TEST 7 This checks the $FF00 decode option selectable in the command
register. The data transfer should not occur until a WRITE TO $FF00.
After a time out subroutine executes, the program checks to see that the
transfer did not occur before the WRITE TO SFFOO.
TEST 8 This checks the interrupt generating capability of the RAM
expander. If an interrupt is generated at the end of the block transfer,
the status register interrupt pending bit goes high.
— 26 —
Section I : Getting Started I
Section 2: 1 764 Test/Demo Software 5
Section 3: RAMDOS II
Section 4: Programmer's Reference Notes 17
Appendix A: 1764 Diagnostic Test Program 25
How to Use This Guide
Section 1 introduces you to the 1764 RAM Expansion Module, and tells
you a little bit about what you can do with it. There are installation
instructions, and a few warnings you'll need to be aware of.
If you are a beginning to intermediate level programmer, you will find
the programs on the 1764 Test/Demo disk indispensible in utilizing the
additional memory. Section 2 concentrates on the software programs
included that were specifically designed for use with your 1764, and
should be helpful for all users, regardless of level of programming
The software also enables you to run the RAMDOS, an operating system
based in the RAM Expander that lets you perform disk operations
quickly and easily. Section 3 provides technical and programming de-
tails on the RAMDOS, for both experts and novices.
If you intend to write your own programs to use the 1764, you will also
find the programmer's reference notes useful. In addition to the mem-
ory map and details about the 1764 registers, this section has a sample
program to load and recall a text screen using the 1764. Section 4 also
includes information about the RAM Expansion Controller and other
technical features of the 1764.
Appendix A: 1764 Diagnostic
The diagnostic test program runs a series of tests, then passes or fails
the 1764 based on its performance.
TEST 1 Checks all memory on the expansion RAM. Four data patterns,
$00, SAA, $55 and $FF, are written in every memory location. The verify
mode of operation checks the data transfer.
TEST 2 To check the RAM expander memory, a checker pattern, $AA and
$55, is written into alternating memory locations. All locations of every
bank are checked.
TESTS 3 and 4 This checks the capabilities for data transfer from the
RAM expander to the C64. Data patterns of SFF's are stored in C64
memory in the following areas:
Data transfers from the RAM expander to the C64 memory fill locations
$1000-$2FFF and $3000-$5FFF with the alternating $55 $AA data pat-
terns. A thorough check of all filled memory in the C64 checks for RAM
corruption in the computer memory. Test 4 repeats this procedure,
using $00 pattern for background fills before the data transfer occurs.
TEST 5 Checks the AUTOLOAD feature of the RAM expander. After a
data transfer, the RAM expander registers should reset themselves to
the setting prior to the transfer. This test checks the Base Address
Register, the RAM Expansion Base Register, the Byte Transfer Length
Register and the RAM Bank Register.
TEST 6 The previous test checks 3 of the 4 transfer modes; this test
checks the remaining transfer mode, RAM expander to C64 transfer with
fixed expander address. A IK byte transfer occurs to C64 locations
— 25 —
Section 1: Getting Started
A RAM Expansion Module is a device that increases the amount of
memory of your computer, giving you more room for storing programs
and data. Your computer has two kinds of memory, Random Access
Memory (RAM) and Read Only Memory (ROM). RAM is used for tempo-
rary storage of data. Programs stored in RAM only stay there as long as
the computer stays on. ROM stores the operating system of your com-
puter, and cannot be changed. The 1764 increases the amount of RAM
of your Commodore 64 or Commodore 64C.
The RAM Expansion Module contains indirectly accessible RAM, mean-
ing that programs stored in the 1764 cannot be executed directly by the
C64. You must first transfer the program into the computer's main
memory, which takes only the time to type in the command.
Keep in mind that RAM is not permanent storage; the information held
in RAM is gone when you turn off the computer. If you want to save
something permanently, make sure you store it on disk.
The 1764 RAM Expander increases the memory capacity of your C64
from 64 kilobytes (64K) by 256K, for a total of 320K. To give you an idea
of how much space your 1764 gives you, an entire word processor takes
up under 30K. A complex game with over 50 levels takes up about the
same amount of memory. So you see how much extra memory your
1764 provides for your use.
But the 1764 gives you more than memory — it gives you speed and
convenience. You won't have to wait for the computer to access the disk
drive for parts of programs, or to use utilities. You can store these in the
extra RAM, for immediate access. You can also use this added speed to
perform animation by cycling sequences of pictures or graphics that you
wouldn't ordinarily be able to manage on a C64 because of memory
limitations. In short, you'll find your 1764 RAM Expansion Module a
useful, convenient addition to your computer system.
Included with your 1764, you'll find a software disk and a new power
supply. The software disk includes utilities and demonstration pro-
grams designed to help you use the capabilities of the RAM Expander
and demonstrate some ways to use the 1764 in programming. Section 2
tells more about the software on this disk.
The power supply is more powerful than the one that originally came
with your computer. Since the RAM Expansion Module hooks directly
into the 64, it draws its power from the computer. The new deluxe power
supply is needed to provide that extra power.
Before you use the 1764, change the power supply you have hooked
to the computer. Plug in the deluxe power supply that came with the
1764 in place of the original power supply that came with your comput-
er. The new power supply will provide the extra power your computer
needs for the 1764. You can use this power supply all the time; you
won't need to hook up the old one again.
Connecting the 1 764 RAM Expander
1 ) Turn off your computer and all peripherals.
2) Replace old power supply with the new one if you have not done so
— 2 —
Under normal operation (no AUTOLOAD, addresss increment), both
address registers point to the next sequential memory location outside
the selected transfer range at the end of the transfer. This is true for any
mode and applies to both base address pointers except one that is held
fixed. The bank pointer is also updated (if necessary) at the end of the
transfer. Also note that under normal operation, the byte counter decre-
ments to the value 1. Care should be taken, therefore, to check the
transfer complete bit in the status register and not rely on the byte
counter value to indicate an end to the transfer condition. A byte
counter of results in a transfer of a full 64 K bytes. Again, wrapping
occurs in all modes of operation.
— 23 —
AUTOLOAD— When you select this option in the command register, the
C64 base address registers, the expansion memory base address regis-
ters, the expansion memory bank and the byte counter registers at the
end of a transfer are automatically reloaded.
This is useful if one operation is to be executed repeatedly on one
particular block of data. Note that if AUTOLOAD is selected in verify
mode, the address where the verfiy error occurred is lost. Ordinarily,
upon finding a verify error, the REC halts the DMA cycle and both
address registers and the bank register point to one location above the
address that failed.
Address Control— Another special feature of the REC is the ability to
hold a source and/or destination fixed in any mode. This is accom-
plished by setting the appropriate bits in the address control register
($0A). The default is that addresses will increment for both source and
destination. It is possible, with a fixed C64 address, to DMA to any I/O
Interrupts— An interrupt can be generated on an end of block condition
or verify error by enabling interrupts and setting the corresponding
mask bits in the interrupt mask register ($09). In either case, the
corresponding flag is set in the status register. Interrupt flags are
cleared upon reading the status register. The interrupt mask register
bits stay as they were before the interrupt/clear sequence. For proper
operation, the status register ($00) must be read at least once before a
DMA is initiated with interrupts enabled. It is important to clear out the
previous status before any mode is used with the interrupt option.
If a specified address range exceeds the address range in the selected
expansion bank, a 'wrap' occurs into the next bank. This happens
whenever the given byte counter exceeds the number of bytes left in the
selected bank. The C64 side always wraps to the beginning of the same
— 22 —
3) Insert the 1764 into the Expansion port on the back of your Commo-
dore 64 or 64C.
Remember the 1 764 was designed only for the 64, and can NOT be used
with the Commodore 128.
4) Turn the computer and all peripherals back on.
Your expansion module is now ready to use.
— 3 —
REC Command Register
Status Register — Read Only
7 - Interrupt Pending 1 = Interrupt waiting to be serviced
6 - End of Block I = Transfer complete
5 - Fault | = Block verify error
4 - Size 1 = 256K
3-0 - Version
Note: Bits 7-5 are cleared when this register is read
Command Register — Read/Write
7 - Execute I = Transfer per current config
6 - Reserved
5 - Load 1 = Enable AUTOLOAD option
4 - FFOO I = Disable FF00 decode
3 - Reserved
2 - Reserved
1 - Transfer type 00 = Transfer C64 > RAM module
01 = Transfer C24 < RAM module
10 = Swap C64 <> RAM module
1 1 = Verify C64 — RAM module
C64 Base Address. LSB — ReadAVrite
Lower 8 bits of base address. C64
C64 Base Address, MSB— Read/Write
Upper 8 bits of base address, C64
Expansion RAM address, LSB — ReadAVrite
Lower 8 bits of base address, expansion RAM
Expansion RAM address. MSB — Read/Write
Upper 8 bits of base address, expansion RAM
Expansion RAM bank— ReadAVrite
Expansion RAM bank pointer.
Bits 2 (MSB) to (LSB} are significant
Transfer Length. LSB — ReadAVrite
Lower 8 bits of the byte counter
Transfer Length, MSB— ReadAVrite
Upper 8 bits of the byte counter
Interrupt Mask Register— ReadAVrite
7 - Interrupt enable 1 = Interrupts enabled
6 - End of Block mask 1 = Interrupt on end of block
5 - Verify error 1 = Interrupt on verify error
Address Control Register — ReadAVrite
0.0 = Increment both addresses (default)
0.1 = Fix expansion address
1.0 = Fix C64 address
1.1 = Fix both addresses
Note: The base address of the REC registers in the C64 memory map is
DF00 in I/O space. The addresses of the REC registers can be obtained
by adding the value in the Address column in the above figure to the
base address of DF00.
— 21 —
avoid a bleed-through if you try to write to ROM. The Commodore 64
Programmer's Reference Guide thoroughly explains these topics.
The REC has four primary operating modes:
1) Transfer a block of data from main memory to expansion memory
2) Transfer a block of data from expansion memory to main memory
3) Exchange a block of main memory with a block of expansion memory
4) Verify a block of main memory with a block of expansion memory
The REC has several internal registers which can be used to set up a
particular operating mode. Modes can be selected by setting the appro-
priate bits in the command register (see Figure 4.3). The starting C64
address, expansion RAM address, expansion RAM bank and number of
bytes are all programmable values.
Direct Memory Access Operation
Direct Memory Access (DMA) is the process the REC uses to transfer
data to and from the computer's memory. During DMA, the C64's
computer processor is temporarily halted so the REC may access the
There are two different events which cause the REC to begin a transfer
1 ) If the FFOO option in the command register ($01 ) is disabled, the DMA
begins right after the execute bit is set in the command register.
2) If the FFOO option is enabled, the DMA begins immediately after a
write to address FFOO is detected - providing the execute bit was
previously set in the command register.
The prupose of the FFOO option is to allow the REC to access the RAM
beneath I/O space. The REC registers are I/O mapped on the C64
expansion bus. which means that, without the FFOO option, I/O space
would be enabled when DMA was initiated. This option, therefore,
allows the user to bank out the the C64 I/O space, replacing it with RAM,
before the DMA takes place. The FFOO option is cleared each time it is
— 20 —
Section 2: 1764 Test/Demo Software
Even if you know nothing about writing programs or memory maps, you
can do a lot with your RAM Expander by running the programs on the
Test/Demo software disk. You can install the RAM Expander, the RAM
operating system, transfer information from disk into RAM, run anima- 7
tions, use your 1764 with the GEOS software package, and more.
The software disk that came with your RAM expander contains programs
for the following applications:
• DOS wedge
• File copying
• Change unit numbers
• Animated sequences (pound and globe)
• Diagnostic testing
• GEOS configuration (on the flip side of the disk)
All of these programs are explained in this section except RAMDOS and
The RAMDOS is an elaborate 1764-based disk operating system. It is
explained in detail in Section 3 of this manual.
The GEOS configure program is not part of the demo software. It is
located on the flip side of the disk. This is used with the GEOS operating
system, and creates an icon for the RAM expander so it can be easily
used with GEOS. There is a separate set of instructions (included in this
The rest of the programs can be loaded from the Startup Menu.
Loading the Startup Menu
The best way to get started with your RAM expander is to load the
Startup Menu from the disk, which lets you select any of the programs
LOAD ,8 <RETURN>
— 5 —
The program to load the Startup Menu is the first program on the disk.
The Startup Menu lets you automatically load the specific program you
select when you enter a number. The Startup Menu options:
1 INSTALL RAM DISK
2 INSTALL DOS WEDGE
3 FILE COPY UTILITY
4 CHANGE UNIT NUMBERS
5 RAM-PAK TEST PROGRAM
6 RAM-PAK POUND DEMO
7 RAM-PAK GLOBE DEMO
Installing the DOS Wedge
The DOS wedge adds commands to C64 BASIC 2.0. These commands
make it easier to display directories, send instructions to disk drives,
and manipulate files. All commands in the DOS wedge may be used
with the 1541/1571 series of disk drives, as well as the 1764 RAMDOS.
You can load the DOS wedge by selecting Option 2 from the Startup
Menu. After you select option 2, the wedge boot message and help
The help screen lists syntax for commands you can use. This typical
form for a DOS command is:
Character <Unit #,> <Filename>
The unit number is optional. If there is no unit number specified in the
command, the last unit number referenced is assumed by the DOS.
The wedge symbols you can use and examples of syntax are displayed
on the help screen.
DOS Wedge Technical Information
The DOS wedge replaces DOS 5.1, which was located at SCC00-SCFFF in
the C64 memory. The 1764 DOS wedge is located at $CC00-$CEFF. It
interfaces via IERROR vector in BASIC 2.0. Note that DOS 5.1 is incom-
patible with 1 764 DOS.
— 6 —
In order for a safe transfer, you must be aware of the C64 memory map.
You are moving blocks of data in and out of main and expansion
memory, so you must know the correct addresses to retrieve the blocks
of data you intend to and store them in the proper places. You'll have to
be careful not to put things in memory where they don't belong, e.g.
over another program or memory allocated for a hardware function. If
you transfer data into an area that is already occupied by a program or
other data, you will overwrite the original data, which may affect the
success of the transfer.
All the standard rules for C64 banking and I/O apply for the 1 764 as well.
For example, you may have to swap out the ROM to use the RAM, to
8K KERNEL ROM
4K I/O or RAM
^ DOS INTERFACE PAGE
8K BASIC ROM
Figure 4.2 C64 Memory Map
— 19 —
Sample Program: Storing and Retrieving
a Text Screen
Here's a functional example of how to change the REC register values in
a program to perform memory manipulations using the 1764. This
program lets you save and retrieve a screen of text to and from the
(SDFOO = REC IN I/O SPACE)
($400 = C64 TEXT SCREEN)
REM SAVE TEXT SCREEN
BA= 13*4096+ 15*256
3,4:REM CPU ADDRESS
40 POKEBA+4,0:POKEBA +
5,0:REM DISK ADDRESS
50 POKE BA + 6.0:REM DISK
8.4:REM NUMBER OF BYTES
POKE BA + 9,0:REM RESET INTERRUPT CONTROL BITS
POKE BA + 10,0:REM INCREMENT BOTH REGISTERS
POKE BA + I,252:REM SAVE SCREEN
PRINT THE SCREEN IS SAVED'
($000 = EXPANSION RAM ADDRESS)
($000 = EXPANSION RAM BANK)
(1024 BYTES = SIZE OF SCREEN)
1 10 PRINT 'PRESS A KEY TO RETRIEVE'
120 GETA$:IFLEN(A$) = THEN GOTO 120
130 POKE BA+2,0:POKE BA+3.4:REM CPU ADDRESS
140 POKE BA + 4,0:POKE BA+5,0:REM DISK ADDRESS
150 POKE BA + 6.0:REM DISK BANK
160 POKE BA + 7.0:POKE BA + 8,4:REM NUMBER OF BYTES
170 POKE BA + l,253:REM READ SCREEN
Line 20 specifies the BASIC address for the beginning of the REC
registers. The rest of the program utilizes this value in the POKE
statements. Line 30 POKEs the address of the text screen. Lines 40 and
50 set the RAM expander address and bank, respectively. Line 60 POKEs
the number of bytes to transfer, which is 1024 for the entire screen of
text (only 1000 are actually used for the text screen). Line 70 resets the
interrupt control bits. Line 80 specifies both C64 and REC address
registers are to increment, and line 90 actually performs the 'save,'
storing the text screen in the 1764 memory area.
Lines 130 to 160 are preparation for recalling the screen from RAM, and
line 170 'loads' the screen.
File Copy Utility
Option 3 is a very handy utility, which you can use to copy files from
your disk drive to RAM, from RAM to disk drive, or from one disk drive to
The file copy reads a disk drive file (or files), and then stores the block of
information in the RAM expander. That information can now be used
immediately when you recall the file. The file still remains on disk, but is
now accessible within the computer's memory. Remember that the file
is available, but not automatically loaded up when it sits in RAM. You
still have to load and run the file as you would from a disk drive. The
difference is the speed at which the program is loaded.
Note: This program can copy PRG, SEQ, REL and USR files.
Load the file copy program by selecting option 3 from the Startup Menu.
At the first two prompts, specify your SOURCE unit number and DESTI-
NATION unit number. If you are copying a file from a disk in the drive to
the RAM expander memory, your source is unit 8 and destination is unit
9 (assuming you installed the 1764 as unit 9).
Then you are prompted:
ENTER TEMPLATE OR <RETURN> ?
If you press the <RETURN> key, the entire directory is read, and you
are asked, one file at a time, whether you want to copy that particular
file, Answer Y or N for each. After the last file, you are asked CONTINUE?
(Y/N): If you still wish to copy the files, answer Y. If you've changed your
mind, answer N.
Instead of pressing <RETURN>, you could enter a template, either a
wild card name (like BAS.*) or an asterisk. Typing * loads everything
from the directory and skips to the CONTINUE? prompt. Answer N to
abort, or answer Y to copy the entire contents of the disk into RAM.
After the copying is completed, you are prompted MORE? (Y/N) for
additional files to copy.
— 7 —
Change Unit Numbers
Sometimes you'll need to change the unit numbers of the 1764 or disk
drive. Even though you can choose the unit number when you install
the 1 764, you may find it necessary to change to a different number. You
may want the RAM expander to be unit number 8 when you no longer
need to use a disk drive.
Option 4 of the Startup Menu is used to change unit numbers. It's pretty
straight-forward: you are asked for the old number of the unit you want
to change, then the new number. The change is almost instant, and a
line describing the unit type and DOS. An initialization message (DOS
error #73) lets you know the change is complete.
You are prompted for additional changes. If you answer N. you exit the
The file copy program provides you with one way to store data in the
RAM expander for your convenience. For example, you can load a game
into the 1 764 by copying the files. Some games utilize the unit number 8
in their code, and you must re-number the 1 764 as unit 8 after you copy
the file. Here's the procedure to follow to load such a game:
Install the RAM expander as unit 9 using option I of the Startup Menu.
Answer Y to initialize the 1764.
Load the File Copy Utility by selecting option 3 from the Startup Menu.
When the prompt ENTER TEMPLATE OR PRESS <RETURN> is dis-
played, change the disk in the drive to the one you wish to load. Then
type * <RETURN> to copy every program on the disk.
There is a brief pause while the directory of the disk is read from the
drive into the RAM. At the prompt CONTINUE? (Y/N), answer Y, which
begins the copying process. Had you answered N, no files would have
After the programs have been stored in the RAM expander, answer N to
the MORE? prompt, unless there are additional files you want to copy.
Now do a directory for unit 9 (to make sure the programs are all in RAM)
— 8 —
Section 4: Programmer's Reference
Memory transfers involving the 1764 are accomplished through the
RAM Expansion Controller (the REC), which is an I/O device. You cannot
directly access the RAM in the 1764. Instead, you instruct the REC to
transfer data between the 1764 memory and C64 memory. This may be
accomplished using POKEs or via machine language.
The demo programs and the ones you'll write set the REC registers
directly. This type of memory transfer is known as Direct Memory Access
(DMA). To see examples of this process, look at the programs on the
Remember that you can use either DMA or RAMDOS — they are NOT
Figure 4.1. Illustration of REC function
— 17 —
Change disks back to the 1 764 Test/Demo Disk.
If the unit number is referenced in the program, there's one more
change you have to make. Since the 1764 is installed as unit 9, that is
where the program is now. However, many programs reference unit
number 8 in the code. In this instance, change the unit number of the
1764 from 9 to 8, using option 4 of the Startup Menu.
Perform a directory for unit 8 (which is now the 1764). You should get
the same listing as you did when you ran a directory for unit 9.
Load and RUN the program from the RAM expander, and it will begin
1764 Diagnostic Test
Option 5 is a test to check if the 1764 is operating properly. The test
wipes out everything in RAM storage, and you are given a chance to
abort the test. It takes about one minute for the test to be completed.
When the test is done and the 1764 passes, the screen looks like this:
256K EXPANSION RAM TEST
After the test is completed, you may re-run it by pressing the space bar,
or exit by pressing RUN/STOP. Be careful not to press RUN/STOP while
test is running. Full explanations of each of these diagnostic tests can
be found in Appendix B of this manual.
The Animation Demos
The disk contains two animation demos, which you can select from
options 6 and 7 of the Startup Menu. Both programs are documented,
so when you list them, you can see for yourself how the cycling of
images is done.
— 9 —
Option 6 is the POUND demo, consisting of 32 separate images which
are stored and cycled from RAM. GLOBE, option 7, features 36 images.
Both demos work similarly.
DO NOT use option 1 to install the RAMdisk before running either
option 6 or 7. Prompts to install the RAMdisk are included within these
programs. If you install the RAMdisk using option 1, there will not be
enough space left in RAM to load all the images in POUND and GLOBE.
So instead, select option 6 or 7 from the Startup Menu, and when you
are prompted LOAD RAM? (Y/N), so answer Y.
A message then appears on the screen, telling you which image is being
loaded. When all the images are loaded, the animation starts.
Here are what each of the demos should look like on your monitor
If you halt the demo by pressing RUN/STOP RESTORE, you can start it
again by typing 'RUN' <RETURN>. Answer 'N' to the LOAD RAM? (Y/N)
Quitting the Startup Menu
Select option 8 to exit from the Startup Menu and back into BASIC.
— 10 —
The interface block swaps out the DOS, restoring the user's memory
map, and returns control to the caller.
The DOS never creates interrupts. During the time the DOS is swapped
in, IRQ's are disabled, to prevent DOS operation from interfering with
NMI's cannot be disabled. Any NMI code used by your programs should
never access or reference data within the area under DOS control. To
counter this, use a DOS image which does not use memory accessed by
your NMI routine.
Note that the only NMI's caused by the system are for RS-232 and
RUN/STOP RESTORE operation.
Concurrent DOS and RS-232 operation is not possible because of the
time required by the swapping process, which is not interruptable. Do
not attempt to use the RS-232 to receive or transmit while accessing the
If you wish to use the RS-232, be careful not to install the 1764 in
memory used by the RS-232.
RAMDOS intercepts this operation, therefore is unaffected when you
press RUN/STOP RESTORE. During DOS calls, RUN/STOP RESTORE is
disabled. You may have to press these keys several times to get it to
work during intense disk activity.
— 15 —
RAMDOS Software Technical Details
The RAMDOS software comes in two parts:
where xxxxxx represents the date the software was generated at Com-
RAMDOSxxxxxx.BAS is a small BASIC program that guides the user
through the process of installing the RAMDOS into the C64 kernel. It
provides workarounds for more advanced users should software incom-
patibility problems arise.
RAMDOSxxxxxx.BIN is the actual RAMDOS binary code which is loaded
into the C64 RAM by the RAMDOSxxxxxx.BAS program. After loading, it
is transferred to the REC (RAM Expansion Controller; see Section 4 for
detail), thereby freeing up C64 memory for other uses.
DOS installation overwrites system memory. Once the DOS is installed,
that system memory is again free for usage, with two exceptions:
1) Indirection vectors — These vectors now point to the DOS interface
block, and the DOS interface block contains the vectors' former values.
2) DOS interface block— This page of code may be installed on almost
any page in the system provided it is not under any ROMs. The default is
the page starting at $CF00 (HEX).
Execution of System I/O Calls
All system I/O calls are made through the indirection vectors which
point to the DOS interface block. Code in the interface block determines
whether the call is for the 1764 or another system device, if the call is
not for the 1764, control is passed on according to the values of the
indirection vectors prior to DOS installation.
If the call is for the 1 764, code in the interface block swaps the DOS with
some normal system RAM and passes control to the DOS. The DOS then
processes your call (which can involve several swaps of DOS and user
RAM), which upon completion returns control to the interface block.
— 14 —
Section 3: RAMDOS
The 1764 RAMDOS is software which allows the 1764 to emulate a disk
drive. The software is installed into the C64 kernel, causing the C64 to
treat the RAM Expander as an additional disk drive. This dramatically
increases the speed of disk operations.
RAMDOS is a compatible subset of the 1 54 1/1 571 disk drive operating
system. In effect, RAMDOS is a DOS without disks. The RAMDOS con-
sists of two programs, which in effect allow you to use the 1 764 as a disk
drive. It is much faster, however, because once the program is held in
the extra RAM made available by the 1764, it's no longer necessary to
access the disk drive; every part of the program is instantly available.
Some applications (especially games) may not work with the RAMDOS
installed. This is because the games depend on the physical aspects of
the disk drive, sometimes executing proprietary code within the disk
Those applications that directly read and write tracks and sectors or
attempt to execute proprietary code within the 1 54 1/1 57 1 disk drive
cannot be run properly with 1764 RAMDOS.
RAM Expander Installation
You initiate RAM DOS by selecting option I from the Startup Menu,
installing the RAM Expander.
After the program loads, you are asked for a unit number to give the
RAM expander. Normally, you will install the RAMdiskas unit 9, which is
the default. This allows you to use the filecopy utility on the Test/Demo
disk to copy files into the RAMdisk from a normal disk drive (which
would be unit 8). You can always change the unit number of the
RAMdisk to 8 later, using the change unit number option of the Startup
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While it is possible to make the RAM expander unit 8 (assuming you are
currently using a 'real' unit 8 drive), you should realize that unless you
have previously placed programs on the 1764 or have a second 'real'
drive, you will have nothing to load.
Next, you can specify where the RAMDISK INTERFACE PAGE is to be
installed. Unless you have a good reason for putting it elsewhere in
memory, accept the default, which is 207 (SCFGO). See the technical
information section for further details.
You are then prompted to initialize (clear) the RAM expander. Normally,
you will answer yes (the default, which is Y) to initialize the 1764. If you
wish to retain the information in the RAM expander, answer N.
Always initialize the RAMdisk after power-up. If your computer has
crashed or been reset via external hardware, you may use this option to
reinstall the RAM driver without losing any information in the RAMdisk.
Once the RAMDOS is installed, you can press any key to return to the
Startup Menu, unless the 1764 is installed as unit 8 (in which case the
program simply ends).
Using the RAMDOS
The RAMDOS behaves like any normal disk drive. It has a directory file,
and supports PRG, SEQ, REL and USR files. It has a command channel
and an error channel, just like a 1541 or 1571 drive. However, not all
1541/1571 commands are supported, due to a different track and sector
The following DOS commands are supported:
(only one file; no concatenation)
(closes all files)
(used for REL files)
(same as init)
(same as init)
(set unit number, where n = unit number)
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The following DOS commands are NOT supported:
M-W Memory-Write (see note below)
Note: The M-W command may be used to change the unit number of
the disk drive by using it to write to locations 1 19 or 120. The RAMDOS
designates this single area to write to. Attempts to write to different
areas in RAMDOS memory are trapped as syntax errors. Note that the
colon is mandatory.
1541/1571 DOS Emulation
The following 1541/1571 operations are emulated by 1764 DOS.
• The DOS supports fifteen concurrent channels, specified by the sec-
ondary address. Channels and 1 are treated like channels 2-14.
Channel 15 is the command/error channel.
• All accesses to the directory file are treated as the interpreted ver-
sion, which has a memory format similar to a BASIC program (i.e.,
line numbers and links are included).
• Wild cards are supported.
• Save with replace is supported.
• DOS supports file level activity. Direct access to tracks and sectors is
• PRG, SEQ, REL, and USR file types are supported.
• The DOS interface to the kernel is through the standard indirection
vectors for the following standard kernel calls:
OPEN, CLOSE. CHKIN, BASIN, BSOUT, GETIN, LOAD SAVE, INMI
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