> Dan was nice enough to send me a partly commented copy of the disassembled
> SC-BIOS. Currently I'm trying to find out what the rest of the code does,
> but there is something I don't understand. In the SC-BIOS there are read
> accesses to $029c and read and write accesses to $029d. $029c seems to
> work similar to INTIM, but I have no idea what $029d is for. Are they
> undocumented RIOT ports or would it be possible, that the SC maps some
> of its ports there? Does anyone have an idea?
As I recall there are several "copies" of the registers that end up
doing the same thing on the 2600. Here's the information from a data
sheet on the RIOT:
OPERATION RS' RW A4 A3 A2 A1 A0
-------------------------------------------------------
Write RAM 0 0 - - - - -
Read RAM 0 1 - - - - -
Write DDRA 1 0 - - 0 0 1
Read DDRA 1 1 - - 0 0 1
Write DDRB 1 0 - - 0 1 1
Read DDRB 1 1 - - 0 1 1
Write Output Reg A 1 0 - - 0 0 0
Read Ouput Reg A 1 1 - - 0 0 0
Write Output Reg B 1 0 - - 0 1 0
Read Ouput Reg B 1 1 - - 0 1 0
Write Timer 1T 1 0 1 (a) 1 0 0
Write Timer 8T 1 0 1 (a) 1 0 1
Write Timer 64T 1 0 1 (a) 1 1 0
Write Timer 1024T 1 0 1 (a) 1 1 1
Read Timer 1 1 - (a) 1 - 0
Read Interrupt Flag 1 1 - - 1 - 1
Write Edge Detect Ctrl 1 0 0 - 1 (b) (c)
Notes:
- = Don't Care
(a) = 0 to disable interrupt from timer to IRQ'
= 1 to enable interrupt from timer to IRQ'
(b) = 0 to disable interrupt from PA7 to IRQ'
= 1 to enable interrupt from PA7 to IRQ'
(c) = 0 for negative edge-detect
= 1 for positive edge-detect
--------------------------------------------------------------------------
Bradford W. Mott (bwmott@xxxxxxx) Computer Science Department
http://www4.ncsu.edu/~bwmott/www North Carolina State University
--------------------------------------------------------------------------
--
Archives (includes files) at http://www.biglist.com/lists/stella/archives/
Unsub & more at http://www.biglist.com/lists/stella/
