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Operating System Register Table
RCA COSMAC VIP Instruction Manual
Memory Register Memory Register
Address Byte Address Byte,
0XB0 0XC0
0XB1 0XC1
0XB2 0XC2
0XB3 R3.0 0XC3 R3.1
0XB4 R4.0 0XC4 R4.1
0XB5 R5.0 0XC5 R5.1
0XB6 R6.0 0XC6 R6.1
0XB7 R7.0 0XC7 R7.1
0XB8 R&0 0XC8 R8.1
0XB9 R9.0 0XC9 R9.1
0XBA RA.0 0XCA RA.1
0XBB RB.0 0XCB RB.1
0XBC RC.0 0XCC RC.1
0XBD RD.0 0XCD RD.1
0XBE RE.0 0XCE RE.1
0XBF RF.0 0XCF RF.1
0X = 07 for 2048-byte RAM
0X = 0B for 3072-byte RAM
0X = 0F for 4096-byte RAM
R5 = CHIP-8 language program counter
RA = CHIP-8 language I pointer
R3 = Machine Language Subroutine Program Counter
Operating System Summary
1. RUN up with key C pressed selects operating
system at 8000.
2. Enter four-digit address followed by mode digit: 5.
A MR (Memory Read)
0 MW (Memory Write)
B TR (Tape Read)
F TW (Tape Write)
3. CDP1802 microprocessor registers are stored as
shown in table above. They may be examined after
a program is run by using operating system mode A.
4. Mode 0 can be used to insert temporary stops in a
program for debugging purposes. Insert a
"branch-to-itself" instruction at the desired stopping
point.
The operating system uses the top 84 bytes of RAM
(0XAC-0XFF). Avoid using these byte locations in
your programs.
6. The operating system searches for and uses the top
(highest) 256-byte page of on-card RAM. When
RUN is flipped up to execute a program, beginning
at 0000, the following initial conditions exist:
P=0, Q=0, R0=0000, and R1 =0XFF where 0X highest
page of on-card RAM.