33
Rev NR
D4
Measure Channel 4 Clock
D5
Reserved (Unused)
D6
Status Word Readback Control
0 => Status Word D31-D8 == Measured Channel Value
1 => Status Word D31-D8 == Control Word D23-D0
D7
Post-divider set
0 = Ignore D23-D8 during Command Word Write
1 = Set Channel Post-Dividers from D23-D8 during Command Word Write
D11-D8
Channel 1 Post-Divider
D15-D12
Channel 2 Post-Divider
D19-D16
Channel 3 Post-Divider
D23-D20
Channel 4 Post-Divider
D31-D24
Reserved (Unused)
Status Word (Read Only)
D0
Program Oscillator Done
0 = Oscillator Programming in progress.
D1
Program Oscillator Error
1 = Oscillator Programming Error has occurred.
D2
Clock Measurement complete.
0 = Clock Measurement in progress.
D7-D3
Reserved (Unused)
D31-D8
If Command Word D6 = 0,
Measured Channel Clock Value
If Command Word D6 = 1,
Control Word D23-D0
Channel Clock Post-Dividers:
The Control Word defines 4 fields for Channel Clock Post-dividers. These post-dividers will further divide down
the input clock from the programmable oscillator to provide for slow baud rates. Each 4 bit field will allow a post
divider of 2^n. For example, if the post-divider value=0, the input clock is not post-divided. A value of 2 will
provide a post-divide of 4 (2^2). This will allow for a post-divide value of up to 32768 (2^15) for each input clock.
Bit D7 of the Control word qualifies writes to the post-divide registers. This allows other bits in the command
register to be set while the post-divide values are maintained.
Channel Clock Measurement:
The Control Word defines 4 bits which will select one of the 4 channel clocks (input clock + post-divide) for a
measurement. This will allow the user feedback as to whether the programmable oscillator was programmed
correctly. To measure a clock, select the clock to measure in the Control word, and also clear Bit D6 to allow for
readback of the result. Read back the Status Word until D2 is set. Status Word D31-D8 should contain a value
representing 1/10 the measured clock frequency (Value * 10 = Measured Frequency in MHz). Keep in mind that this
value will not be exactly the programmed frequency due to the 100ppm (0.01%) accuracy of the on-board reference.
