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11. COSMAC VIP Operation
COSMAC VIP is operated with the RUN switch and
hex keyboard. The PWR light shows that power is on.
The Q light is activated by various programs. A tone is
sounded whenever the Q light is on. The TAPE light
glows when cassette input data is present. When using
COSMAC VIP, always start with the RUN switch in the
down (or reset) position. Flipping the RUN switch up
initiates execution of machine language programs
beginning at memory location 0000. If you have
previously stored the CHIP-8 Ian_ guage interpreter
program at locations 0000-01FF, execution of a program
written in this language will begin at 0200. To manually
terminate execution of any program, flip RUN down.
Using the Operating System
With COSMAC VIP you can load programs into
memory from the hex keyboard or cassette recorder,
record the contents of memory on cassettes, show the
contents of memory bytes in hex form on the display,
and examine the contents of CDP1802 microprocessor
registers. These functions are performed with the aid of a
special program called an operating system. This
operating system is contained in a ROM so that it's ready
to use as soon as power is turned on. It is located at
memory locations 8000-81FF. A machine code listing
and summary of this operating system is provided in
Appendix B.
To use the operating system hold key C down on the
hex keyboard when you flip RUN up. You will hear a
tone. Release key C and you're ready to use the
operating system.
After selecting the operating system you can do four
different operations as shown in the following table:
9
KEY OPERATION
0
A
F
B
MW (Memory Write)
MR (Memory Read)
TW (Tape Write) TR
(Tape Read)
For any of these operations you must first enter a
memory address. Enter the 4 hex digits of any memory
address using the hex keyboard (most significant digit
first). You will see the address at the lower left of the
screen and the byte contained in that address at the lower
right. Remember that addresses and bytes are always
entered and shown in hex form. Suppose you entered
0200. You will see 0200 at the bottom left of the screen
and the byte stored at 0200 at the lower right.
Memory Write
If you want to change this byte, press the 0 key. Now
press two digits of the new byte (most significant digit
first) and it will be stored at 0200 replacing the original
byte. You will see this change on the screen. If you enter
another byte it will be shown and stored at the next
higher address in sequence (0201 in this example). You
can load any, sequence of bytes directly from the hex
keyboard in this manner. If you make a mistake, flip
RUN down. With key C pressed, flip RUN back up.
Enter the address at which you made the error. Press key
0 and resume entering your program.
Note the random bit pattern on the screen above the
hex display. This pattern is the binary data