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contained in the last 256-byte page of the on-card RAM.
If you have a 2048-byte RAM, you are seeing locations
0700-7FF on the screen. Bit 7 of the byte at 0700 is in
the upper left comer. Try storing a sequence of eight AA
bytes followed by eight 55 bytes starting at location
0700. Keep repeating this sequence to draw a
checkerboard pattern on the screen. There are 32 rows of
spots on the screen. Each row represents 8 memory bytes
(64 bits). Locations 0700-0707 are shown in the top row,
0708-07OF in the next row down. Draw a bit map on
paper and you can construct pictures on the TV screen by
entering the proper byte sequences. The byte pattern for
displaying the word COSMAC is shown in Appendix A.
Memory Read
Suppose you wish to examine the contents of a
memory location. Flip RUN up while pressing key C.
Enter the address of the location you want to examine.
Press key A for the Memory Read mode. You will see
the memory address and the byte stored at that address
on the screen. Press any hex key to step through memory
and see the contents. Memory locations examined are
left unchanged. If a program doesn't run properly you
can use this mode to verify that it was stored correctly in
memory.
You can now enter and run the short beeper program
shown in Appendix A. Flip RUN up with key C pressed.
Release key C and enter address 0000. Press key 0 to
select the Memory Write mode. Now enter the beeper
program one byte at a time using the hex keyboard. Flip
RUN down to reset the computer. Flip RUN up to
execute the beeper program you just loaded into
locations 0000-OOOC. You can load and run any
COSMAC VIP program in this manner. For most of the
game programs you will first have to load the CHIP-8
interpreter (Appendix C) into locations 0000-OIFF
followed by the game program starting at location 0200.
Tape Write
Any program you load into memory will be lost when
you turn off power. Unless it is safely stored, you will
have to key it in by hand again the next time you want to
use it. The cassette interface is provided so that after
keying in a program you can then record it on an audio
cassette; and when you want to use the program again,
all you have to do is play it back into the memory from
the cassette. This playback usually takes less than 30
seconds.
The COSMAC VIP cassette interface was designed to
work with most standard audio cassette recorders.
Panasonic models RQ-309DS, RQ-212D, and RQ-413S
have yielded satisfactory results as has the Sony
RCA COSMAC VIP Instruction Manual
TC-150. In general, better quality recorders provide
more reliable operation.
Your tape recorder must have an 8-ohm earphone or
external speaker jack and a microphone input jack.
Connect the cassette recorder to the COSMAC VIP
tape-in tape-out pads on the right-hand side of the card as
shown in the cassette attachment diagram in Appendix
A.
After properly connecting your cassette recorder you
can try recording and playing back a cassette using the
operating system as described below. Follow the cassette
recording guidelines provided in Appendix A for best
results. If you run into trouble, use the cassette phase and
data test procedures described in Appendix A for
troubleshooting.
The memory is divided into 256-byte pages for
recording. You can record 1 to 15 consecutive pages on
tape. The low-order byte of your starting address should
be 00. Select the operating system by holding key C
down while flipping RUN up. Enter the 4-digit address
of the first page to be recorded on tape. Press key F and
you're ready to record. Rewind a blank cassette and place
your cassette unit in the record mode. Wait about 10
seconds and tap the hex key that represents the number
of pages you want to record on tape. The screen will go
blank and you'll hear a tone while recording. When the
specified number of pages has been recorded on the
cassette, the tone will end and the last memory byte
recorded on tape will be shown on the screen.
Tape Read
To load memory from a previously recorded cassette,
first select the operating system (RUN and key C). Enter
the memory address of the first page to be loaded
(usually 0000). Press key B to select the Tape Read
mode. Rewind and play the cassette. Immediately press
the hex key representing the number of pages you want
to load into memory from the cassette. The tape recorder
tone control should be set to maximum high. The volume
control should be set for a steadily glowing tape light
when data is being read from the tape. The screen will go
blank while the program is loaded from the tape into
memory. It will show the last byte loaded into memory
at the end of loading.
If the Q light and tone come on while a tape is being
read, an error occurred. Flip RUN down, rewind the
cassette, and try again. You may h ' ave to readjust the
cassette volume control. Be sure that the cassette
contains at least as many pages as you specify to be
loaded. For most of the game programs, load the
CHIP-8 interpreter program (Appendix C) into 0000-