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Turbo PMAC PCI Lite
E-Point Jumper Descriptions
29
E3 - E6: Servo Clock Frequency Control
The servo clock (which determines how often the servo loop is closed) is derived from the phase clock (see
E98, E29 - E33) through a divide-by-N counter. Jumpers E3 through E6 control this dividing function.
E3
E4
E5
E6
Servo Clock = Phase Clock
Divided by N
Default and Physical Layout
E3 E4 E5 E6
LOCATION A8 A8 A7 A7
ON
ON
ON
ON
N = divided by 1
OFF
ON
ON
ON
N = divided by 2
ON
OFF
ON
ON
N = divided by 3
OFF
OFF
ON
ON
N = divided by 4
Only E5 and E6 ON
ON
OFF
ON
ON
N = divided by 5
OFF
ON
OFF
ON
N = divided by 6
ON
OFF
OFF
ON
N = divided by 7
OFF
OFF
OFF
ON
N = divided by 8
ON
ON
ON
OFF
N = divided by 9
OFF
ON
ON
OFF
N = divided by 10
ON
OFF
ON
OFF
N = divided by 11
OFF
OFF
ON
OFF
N = divided by 12
ON
ON
OFF
OFF
N = divided by 13
OFF
ON
OFF
OFF
N = divided by 14
ON
OFF
OFF
OFF
N = divided by 15
OFF
OFF
OFF
OFF
N = divided by 16
Note:
The setting of I-variable I10 should be adjusted to match the servo interrupt cycle
time set by E98, E3 – E6, E29 – E33, and the crystal clock frequency. I10 holds
the length of a servo interrupt cycle, scaled so that 8,388,608 equals one
millisecond. Since I10 has a maximum value of 8,388,607, the servo interrupt
cycle time should always be less than a millisecond (unless the basic unit of time
on PMAC is something other than a millisecond). To have a servo sample time
greater than one millisecond, the sampling may be slowed in software with
variable Ix60.
Frequency can be checked on J4 pins 21 and 22. It can also be checked from software by typing
RX:0
in
the PMAC terminal at 10-second intervals and dividing the difference of successive responses by 10000.
The resulting number is the approximate Servo Clock frequency kHz.
Note:
If E40 – E43 are not all ON, the phase clock is received from an external source
through the J4 serial-port connector, and the settings of E3 – E6 are not relevant.
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