PC Chips M571 V70A motherboard and JP11
---------------------------------------
***** (untested information) *****
I suspect that JP11 on the PC Chips M571 motherboard disables the onboard sound, ie OUT = enabled, IN = disbled.
While this can be done via the BIOS setup, probably by programming the CM8330 chip's registers, I believe the hardware solution involves disabling the chip via the higher order address bits.
Some reverse engineering of the M571 produced the following:
___ JP11 ___
+5V O----|___|----O O----|___|---|
1K | 4K7 _|_
| =
|
|---> to "XAcdef" pin of sound chip
The XAcdef pin is described in the C-Media data sheet as the "address enable for A12 to A15". No more detail is given. Note that 12, 13, 14, 15 (dec) = C, D ,E, F (hex) respectively. The first twelve address lines (XA0 to XA11)
are bussed to the ISA address lines, SA0 to SA11. Note that the default setting of JP11 is OUT, which places the XAcdef pin at a permanent logic LOW level. I assume that a logic 0 enables the chip.
The C-Media CM8330 application circuit implements this pin as follows:
SA12 -|>|---|
|
SA13 -|>|---|
|------|----> to XAcdef pin of sound chip
SA14 -|>|---| |
| _|_
SA15 -|>|---| | | 4K7
|_|
|
_|_
=
( -|>|- = diode)
This wired-OR configuration places the XAcdef pin in the HIGH state if any of the high order address lines is set. I believe the idea is to prevent the chip from responding to I/O calls to addresses above xFFF (which it doesn't directly decode). By installing a jumper at JP11, the chip is fooled into believing that every I/O call is directed to addresses above xFFF, thus effectively disabling it.
This page was last modified on 17 July
2002