Q-Flex Satellite Modem Installation and Operating Handbook
9-10
X.21 DTE Operation
This has only a clock
to
the modem from the terrestrial equipment. Configure a cable with a
15 pin `D` male at one end (X.21 DTE) and a 25 pin `D` male at the other end as follows:
Min
Req
X.21 DTE
(15 pin D male)
Signal
Description
RS422
Name
Circuit
Number
25 pin
Electrical
Levels
Name
A
B
A
B
DATA CIRCUIT TOWARDS MODEM (TX)
Υ
S
6
13
Clock In
TT
113
24
11
RS422
Υ
R
4
11
Data In
SD
103
2
14
RS422
I
5
12
Sig
’
Valid In
RS
105
4
19
RS422
DATA CIRCUIT FROM MODEM (RX)
Υ
T
2
9
Data Out
RD
104
3
16
RS422
C
3
10
Sig
’
Valid Out
RR
109
8
10
RS422
COMMON LINES
Υ
Sig gnd
8
Signal Ground
SG
102
7
Ground
Υ
Prot gnd
1
Shield / Prot
’
ground
PG
101
1
Screen
Clocking
For the interface to function as X.21, the clocking must be set as follows. The
Tx Clocks
menu should be used to take the single clock from the terrestrial by selecting
Tx Clock In.
The
Rx Clocks
menu should also be set to return Rx data in time with the single Tx Clock
by also selecting
Tx Clock In
. No other combinations will work.
The maximum data rate is 10Mbps (over good quality twisted pair screened cable), but this
rate is reduced as the connecting cables extend beyond 10m. As an estimate, assume the
maximum rate halves as the distance doubles (ie 5Mbps to 20m, 2.5Mbps to 40m etc).
The input clock/data phase is selected automatically, reporting a `Data Marginal` warning
whenever it has to switch phase. If the modem reports Data Marginal frequently then this is
not a modem fault but an indication that you have a clocking problem external to the
modem (ie changing clock/data phase, a problem which would otherwise have caused
untraceable data errors). Check the phase of the
Data In
with respect to the Clock In line.
It is possible to configure the Tx carrier to be switched on and off by the `Sig= Valid In` line
by selecting
Edit->Tx->Carrier
and selecting
RTS enabled
.
P3722 G.703 Interface
The G703 interface supports the following settings.