FORTH for the PC-G850(V)(S)

[robve]

A really nice thing about the PC-G850(V)(S) is that the ROM and RAM addresses are known and included in the excellent PC-G850V(S) User Guide translated by Jack W. Hu.

So let's go forth and put our "Pokecon" to some good use by defining a new Forth850 word TEXT that reads the TEXT editor area to evaluate Forth. In this way we can write Forth code in the built-in TEXT editor and then read it back into Forth:

• write Forth code with line numbers in the TEXT editor
• in Forth enter TEXT to read the source code
  

The TEXT area start- and end-pointers are located in RAM at &H7973-4 and &H7975-6, respectively. The BASIC and TEXT code has a &HFF marker at TEXT start and end. The internal BASIC/TEXT line format is: hi lo len data... &H0D where

• hi is high order byte of line number, hi is &HFF at end
• lo is low order byte of line number
• len is length of the line up to and including the &H0D byte
  

Keeping this in mind, the TEXT word is defined as follows, using EVALUATE to evaluate each line in the TEXT area:

Code:

: TEXT
  $7973 @ 1+ >R
  BEGIN
    R>                  \ -- addr
  DUP C@ $FF <> WHILE
    2+ DUP C@ SWAP 1+   \ -- len addr
    2DUP + >R
    SWAP 1- EVALUATE
  REPEAT
  DROP ;

A minor caveat of using EVALUATE for each line: .( and ( cannot span multiple lines, i.e. a ) must be on the same line.

- Rob