Re: [stella] the B. Watson's problem...

Subject: Re: [stella] the B. Watson's problem...
From: "Eckhard Stolberg" <Eckhard_Stolberg@xxxxxx>
Date: Tue, 21 Aug 2001 20:50:57 +0200
> Are you really trying to read TIM64T or it was just a mistake? Either way,
> would like to know what would happen with this read on a real VCS, because
> PCAE doesn´t seem to care and returns the timer value.

For TIM64T and TIM1T it should be the same as INTIM. For TIM8T and
TIM1024T you would be reading the 'timer overflow register'. I'm
not quite sure what it does, but I think it counts how ofter the
timer has gone from $00 to $FF.

> And since we are in the subject, which PIA registers are accessed with the
> addresses 283,29D,29E and 2A2?

$283 is SWBCNT. It controls the data direction for the console
switches. Since these are hardwired to input on the VCS, you should
set this register to all bits intput.

$29D and $29E are TIM8T and TIM64T with interrupt enabled. The
6507 processor in the VCS can't handle interrupts, so this isn't
really much different from the normal timer registers. However,
since the RIOT keeps the interrupt flag in an extra register
$285, I think), you might be able to do a wait for timer loop
with a BIT instruction, since the timer interrupt flag is at D7.

$2A2 is just a different address for SWCHB.

BTW, where did you find these addresses? Are you currently
working on a disassembly of a VCS game?

Ciao, Eckhard Stolberg

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