Spectracom TPRO-cPCI, User Manual, Page: 35 / 46

TPRO-cPCI/TSAT-cPCI Spectracom Corporation
Synchronizable Timecode Generator User Manual 5-5
5.6 Set Heartbeat Divider
0 x 0040
The Heartbeat is the output of a programmable divider. This command selects the clock
frequency and the counter preset number.
The counter counts from the counter preset number up to maximum count (0xffff). When
maximum count is reached, one Heartbeat pulse is output, and the counter re-loads the counter
preset number. Compute the counter preset number N as follows:
N = 65536 – (F * t)
F is the frequency chosen; t is the Heartbeat interval in seconds.
The permissible range of values for N depends on the clock select. For clock selects 0x0, 0x2,
and 0x3, the permissible range for N is 0x0000 through 0xfffe, inclusive. However, for clock
select 0x1, the permissible range is 0x0003 through 0xfffc, with the further restriction that N
must be evenly divisible by 3.
Set the Heartbeat period as follows. The counter is forced to maximum count each time
synchronization is established. This causes the Heartbeat output to be in sync with the absolute
time.
Bits tbreg_cmd[0] Bits tbreg_cmd[1]
31:16 (unused) 31:04 (unused)
15:00 N 03 Invert(1)/Normal (0)
02 Enable(1)/Disable (0)
01:00 Clock Select
Bits tbreg_cmd[2] Bits tbreg_cmd[3]
31:00 (unused) 31:16 (unused)
15:00 0x0040
The Clock Select field selects F, as follows:
Programmable Range
Clock Sel F Pulse Width Minimum Maximum
0x0 1 * 10
7
100 nS 200 nS 6.55 mS
0x1 3 * 10
6
333 nS 666 nS 21.84 mS
0x2 1 * 10
6
1 µuS 2 µS 65.5 mS
0x3 1 * 10
3
1 mS 2 mS 65.5 seconds
Step size is the same as the Pulse Width.
5.6.1 Examples for Setting the Heartbeat
If the desired Heartbeat interval is 750 uS between pulses, choose (1 * 10
6
) for the Clock Select,
and compute N = 0xfd12:
N = 65536 – (1 * 10
6
)*(750 * 10
–6
)
N = 64786 (base 10) convert to hex: 64786 = 0xfd12