GM P4 $400x regs

[Ludis Langens]

trinity at golden.net (Mike) wrote:
> The control registers of the P4-chipset which are mapped to $400x in all P4s
> I've seen...From some work I'm doing on several PROMs concurrently, I see
> that $4009 is the serial receive register, $400A is the serial transmit
> register and $4007 is the SCCR2 (HC11 $102D) equivalent. $4008 appears to be
> the "SCI" status register.
>
> $4008 appears pretty close to bit-for-bit compatible with the standard HC11
> $102E SCSR register except bit 0. Anyone know what this bit is doing?

Here's what I've figured out from reading the code:

r/w  $4000  SPI data register
r/w  $4001  I/O control register, including SPI control
r/w  $4002  I/O port (probably all outputs)
r/w  $4003  DDR, probably for $4004
r/w  $4004  I/O port
ro   $4005  Free running up counter, probably at 32768 Hz
r/w  $4006  Interrupt time, IRQ when $4006 == $4005  ( maybe <= )
r/w  $4007  SCI control register
ro   $4008  Interrupt source flags
ro   $4009  SCI RxD register
wo   $400A  SCI TxD register
wo   $400B  COP watchdog ($FF)
wo   $400C  COP watchdog ($00)

r/w == read and write, ro == read only, wo == write only

My $4007, $4009, and $400A uses match your findings.  $4008 looks to not
be SCI related at all.  It's use matches the use of a similar register
in the C3 chipset.  This register contains a bit that indicates that IRQ
is asserted.  That's bit zero in $4008.  The other bits help determine
the interrupt source - or what events have happened since the previous
read of this register.  Reading $4008 deasserts IRQ.

Output bits in $4002:
 %10000000  chip select to output only SPI device
 %01000000  chip select to in and out SPI device
 %00001000  chip select to SPI interfaced ADC
 %00000100  chip select to in and out SPI device
 %00000010  IAC phase B output
 %00000001  IAC phase A output

Output bits in $4004:
 %00000100  Enable IAC

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/