Reference Manual
PMAC 2 Software Reference
40 PMAC I-Variable Specifiation
I54 Baud
Rate
Error with
CPU at 40
MHz
Error with
CPU at 60
MHz
Error with
CPU
at 80 MHz
Error with
CPU
at 160 MHz
0 600 0 (Disabled) 0 0
1 900 -0.05% 0 -0.03% -0.01%
2 1200 0 0 0 0
3 1800 -0.1% 0 -0.05% -0.03%
4 2400 0 0 0 0
5 3600 -0.19% 0 -0.10% -0.05%
6 4800 0 0 0 0
7 7200 -0.38% 0 -0.19% -0.10%
8 9600 0 0 0 0
9 14,400 -0.75% 0 -0.38% -0.19%
10 19,200 0 0 0 0
11 28,800 -1.5% 0 -0.75% -0.38%
12 38,400 0 0 0 0
13 57,600 -3.0% 0 -1.5% -0.75%
14 76,800 0 0 0 0
15 115,200 (Disabled) 0 -3.0% -1.5%
CPUs run at 30 MHz, 90 MHz, 120 MHz, or 150 MHz, as well as 60 MHz, also have zero baud
rate errors at all of these baud rates. Some users may want to slow down their CPU frequencies
from the maximum rated frequency in order to get accurate high baud rates.
Because of the nature of the clock generation circuitry, odd values of I54 on a PMAC2 with a
CPU operating at 40 MHz (Jumper E2 OFF) produce non-exact baud rates. The error in baud
rate is small enough that communications should still be valid.
If your host computer baud rate cannot be made to match the PMAC2’s baud rate, either
PMAC2’s baud rate must be changed through the bus communications port, or the PMAC2
must be re-initialized by resetting or powering up with the E3 jumper ON. This forces the
PMAC2 to the default baud rate of 38,400.
I55 DPRAM Background Variable Buffers Enable
Range
0 .. 1
Units
none
Default
0
Remarks
I55 enables or disables the dual-ported RAM (DPRAM) background variable read and
write buffer function. When I55 is 0, this function is disabled. When I55 is 1, this
function is enabled. When enabled, the user can specify up to 128 PMAC registers to be
copied into DPRAM each background cycle to be read by the host (background variable
read) and up to 128 PMAC registers to be copied each background cycle from values
written into the DPRAM by the host (background variable write).
See Also
DPRAM Background Variable Read Buffer (Option 2 DPRAM Manual)
DPRAM Background Variable Write Buffer (Option 2 DPRAM Manual)