GPL Status Byte

[Willsy]

Okay, the GPL status byte at >837C is giving me grief.

 

Thy Hallowed Book of Truth sayeth that thy Holy GPL Byte of Holy Status be it assembled thusly:

 

 

And lo, it was so.

 

Yet hark, verily does thy Book Of Truth refer to an "equal bit" (FCOM, page 260):

 

 

Where ist thou "equal bit"?

 

[ or is the book referring to the eq bit in the 9900? If so, it's a bloody shambles! ]

[+Lee Stewart]

Mark...

 

Equality uses the COND bit---best have a look at the GPL Programmer's Guide in the pinned Development Resources on this site.

 

...lee

[Willsy]

Thanks Lee. Well, the plot thickens... I found this in the ROM after single stepping:

 

0FAA STST 2
0FAC MOV R2,@>837C

 

In other words, the GPL status byte is a copy of the 9900's status register.

 

Well well...

 

The EQ bit in the 9900 is bit 2, which just happens to be the COND bit in GPL parlence. So, you're spot on sir! Thank you. Another mystery solved.

 

Mark

[+Lee Stewart]

You're quite welcome. Maybe different people wrote different sections of the Hallowed Book of Truth, much like the clearly, obviously different styles in chapters of the original TI Forth manual, which I need to get back to editing!

 

...lee