Comtech EF Data SDM-650B User Manual

Page 57

SDM-650B Satellite Modem

Configuration

Rev. 5

3–15

INT/EXT CLOCK

TO CONTROL LOGIC

LOOP TIMING

TO LOGIC CONTROL

TO BUFFER

OPTIONS

SCT

M
O
D
E
M

TX CLOCK

TX DATA

AUTO
CLOCK
SELECT

TO CONTROL LOGIC

LOOPBACK

T
E
R
R
E
S
T
R
I
A
L

EXTERNAL BUFFER CLOCK

INVERT
NORM

TO BUFFER

OPTIONS

RX CLOCK

RX DATA

COMMON EQUIPMENT

MODULATOR

DEMODULATOR

FAULT

RELAYS

CONTROL

LOGIC

RTS TO CTS JUMPER

TTL MODULATOR FAULT

SPARE (RS-232 ONLY)

TTL DEMODULATOR FAULT

DATA BUS TO M & C

Figure 3-5. V.35 Interface Block Diagram

In either case, the phase relationship between the clock and data is not important as long
as the relationship meets the jitter specification. This is because a clock phase correction
circuit is provided, which shifts the clock away from the data transition times.

The clock selection is jumper-selectable at JP1 on the front edge of the board.

• When there is no jitter on the clock source, the Auto setting is used.

• The Normal setting is used when standard specifications on clock and data

relationships exist.

• The Invert mode is used when the incoming clock is inverted from the standard

clock and data relationship.