PMAC-PCI Hardware Reference
Software Setup 59
For a PMAC2 board with a saved value of 0 for I46, the serial baud rate is determined by the
combination of I54 and the CPU frequency on a PMAC2 board as shown in the following table.
These settings maintain backward compatibility.
* Not an exact baud rate
With the Flex CPU, the card number (0 – 15) for serial addressing of multiple cards on a daisy-
chain serial cable is determined by variable I0, even on PMAC(1) boards. This has always been
the case for PMAC2 boards, but with other CPU boards, the card number on PMAC(1) boards
has been determined by the settings of jumpers E40 – E43. Jumpers E40 – E43 on a PMAC(1)
board with the Flex CPU still determine the “direction” of the phase and servo clocks: all of these
jumpers must be ON for the card to use its internally generated clock signals and to output these
on the serial port connector; if any of these jumpers is OFF, the card will expect to input these
clock signals from the serial port connector, and its watchdog timer will trip immediately if it
does not receive these signals.
Configuring PMAC with Option-5C for 80 MHz Operation
On a PMAC with flash-backed main memory, jumper E48 controls the frequency of operation of the
DSP. It can only directly set 40 MHz and 60 MHz DSP operation. On power-up/reset, the DSP,
operating at the crystal frequency of 20 MHz, reads the frequency jumper E48 and writes into its own
PLL multiplier register at X:$FFFD. Bits 0-3 of this word contain a value one less than the multiplier
value (if the frequency is being multiplied by 3, these bits contain a value of 2).
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