Comtech EF Data SDM-9000 - Manual (Page 217)

SDM-9000 Satellite Modem Options
Rev. 4 A–31
A.3 ESC 64 kbit/s Data Option
The two audio channels in the ESC data stream can be replaced with a single 64 kHz
data channel.
The data is transmitted and received on the same connector pins which were used for
audio. The data is electrically similar to the 8 kHz data channel (except for the data rate).
As with the 8 kHz channel, the data transitions on the falling edge of the clock, and is
valid on the rising edge. Setup and hold times for the rising edge are 5 uS.
If byte alignment is required, the 8 kHz clock can be used. The first bit of data is valid
with the first rising edge of the 64 kHz clock following the rising edge of the 8 kHz
clock. The rising edge of the 8 kHz clock should occur within 5 uS of the falling edge of
the 64 kHz clock.
The receive timing is identical to the transmit. Data transitions on the falling edge of the
clock and is valid on the rising edge. If byte alignment is used, the rising edge of the first
64 kHz clock following the rising edge of the 8 kHz clock marks the first data bit.