Reference Manual

Flex CPU Piggyback Board Hardware Reference
Operation of the Flex CPU 9
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.
I54 Baud Rate for
40 MHz CPU
Baud Rate for
60 MHz CPU
Baud Rate for
80 MHz CPU
0 600 Disabled 1200
1 900* (-0.05%) 900 1800* (-0.1%)
2 1200 1200 2400
3 1800* (-0.1%) 1800 3600* (-0.19%)
4 2400 2400 4800
5 3600* (-0.19%) 3600 7200* (-0.38%)
6 4800 4800 9600
7 7200* (-0.38%) 7200 14,400*(-0.75%)
8 9600 9600 19,200
9 14,400*(-0.75%) 14,400 28,800*(-1.5%)
10 19,200 19,200 38,400
11 28,800*(-1.5%) 28,800 57,600*(-3.0%)
12 38,400 38,400 76,800
13 57,600*(-3.0%) 57,600 115,200*(-6.0%)
14 76,800 76,800 153,600
15 Disabled 115,200 DISABLED
* 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.
Operation as a Turbo CPU
When used as a Turbo CPU, the Flex CPU is fully compatible with older CPU designs. It does permit
higher-speed configurations (Option 5Ex at 160 MHz), which offer significantly higher performance both
due to increased operation frequency and added internal memory.
Variable I52 determines the actual operating frequency of the Turbo CPU. The operational frequency is
set to 10MHz * (I52 + 1). I52 should be set to 7 to operate an Option 5Cx board at its maximum rated
frequency of 80 MHz; it should be set to 9 to operate an Option 5Dx board at its maximum rated
frequency of 100 MHz; it should be set to 15 to operate an Option 5Ex board at is maximum rated
frequency of 160 MHz.
I52 is used only at power-up/reset, so to change the operational frequency, set a new value of I52, issue a
SAVE command to store this value in non-volatile flash memory, then issue a $$$ command to reset the
controller.