RCA VIP VP580 - Chip-8 X

Chapter II
CHIP-8X
CHIP-8X
is an expanded version of the original CHIP-8 interpreter which allows
easy control over RCA's new options for the VIP: color card, simple sound, and
expansion hex keyboard. Programs written in CHIP-8X will run on a standard VIP with
none of the options installed, but for full feature use the options will greatly
enhance your enjoyment.
All of the instructions from the original CHIP-8, except BMMM, are valid for
CHIP-8X, and CHIP-8X offers these new instructions:
Instruction
FXF8
FXFB
EXF2
EXF5
BXYO
BXYN
02AO
5XY I
Function
VX ... output port (used to program simple sound)
Input port .. VX (waits for EF4=1)
Skip next instruction if VX= hex keypad 2
Skip next instruction if VX~ hex keypad 2
Set VY color @ VX(I!H), VX+] (NV) (provides low resolution
color 8x8)
N~6, set VY color @ VX, VX+l byte N bytes vertically
(provides higll resolution color 8x32)
Steps background I color ( .. blue ... black .. green .. red .. )
Let VX= VX+VY (hex digits ~~ to 77) (useful for manipulating
the NU, NV parameters for low resolution color)
We will cover the use of these instructions in more detail in the subsequent
chapters. Your first task is to enter the modifications which transform CHIP-8
into CHIP-8X. You begin this process by loading a copy of CHIP-8 into memory from
tape. Loading the first two pages of any CHIP-8 game will give you the proper
memory contents to begin. The new version of CHIP-8X will require three pages of
memory (000~-02FF).
CHIP-8X can be created by modifying the original CHIP-8 interpreter as
follows:
1) Load the original CHIP-8 into M(0000) - M(01FF).
2) Replace original codes with new codes shown below:
(Those memory addresses which must be modified if you relocate this
code to another memory area are flagged with an asterisk.)