TI99: WP and PC

From: Allison J Parent <allisonp_at_world.std.com>
Date: Fri Jan 29 18:03:40 1999

<What are WP and PC w.r.t the 9995? I'm reading the memory map and I don't
<understand what those terms are. A related term seems to be BLWP, which I
<don't understand either. (I'm only a poor 6502 programmer. :-)

OK,

WP... workspace pointer. back when the 9900 was new registers (memory)
really ate up chip space and TI had an archetecture in the 990 minicomputer
where register were in memory instead of in the CPU. So the WP is a pointer
that points to a block of 16 locations in ram that are addressed in
instructions as R0 through R15.

PC is PC just like the 6502. It's the instruction counter.

BLWP is an instruction that does several things.
  
     It branches to a specified address.
     It saves the WP and PC in the R14 and R15 of the new
     workspace.
     It then resumes at the newly specified PC.

Obviously it nees two parameters a new WP and PC. They are specified by
varios means (addressing modes and registers). Think of it as something
like a 6502 call and Push combined though it's more powerful.

Allison
Received on Fri Jan 29 1999 - 18:03:40 GMT