P1440 In X.21 Mode - Paradise Datacom P300-VSAT Installation & Operating Handbook

P1440 IN X.21 MODE

The P300 along with its standard P1440 RS422/V.35/RS232 interface can provide both X.21 DCE and X.21
DTE operation. For X.21 operation the card must be set to RS422 mode, and the Tx & Rx Clocking modes
must be set correctly. With the use of the appropriate adaptor lead (to convert to the X.21 standard 15 pin
D connector), a full X.21 DCE or DTE interface is available.
X.21 DCE OPERATION
This only has a clock from the modem to the terrestrial equipment. Configure a cable with a 15 pin `D`
female at one end (X.21 DCE) and either a 25 pin or 37 pin `D` male (not both) at the other end as follows:
X.21 DCE
Min
(15 pin D female)
Req
Name A
DATA CIRCUIT TOWARDS MODEM (TX)
&
T 2
C 3
DATA CIRCUIT FROM MODEM (RX)
&
S 6
&
R 4
I 5
COMMON LINES
&
Sig gnd
&
Prot gnd
Clocking: IMPORTANT
The interface will not work as X.21 unless you set the clocking correctly ! The Rx Clock Menu is used to
set the source of the single clock from the modem as either Satellite, Internal, or Station Clock. Do not
select Tx Clk In as this does not exist in X.21. The Tx Clocking should simply be set to Rx as the Tx data
is clocked by the same clock as the Rx data.
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 Out line.
By selecting Change, Terr-Intfc, Control Lines it is possible to configure the modem to raise an alarm if
either the `Sig' Valid In` line ( C ) switches to the inactive state. As there is no X.21 equivalent of the RS422
`Device (DTE) Ready In` line (TR), set this to Ignore. It is also possible to configure the Tx carrier to be
switched on and off by the `Sig' Valid In` line ( C ) by selecting Change, Tx, Modulator, Carrier, RTS-
Controlled.
P300H
Signal
Description
B
9 Data In
10 Sig' Valid In
13 Clock Out
11 Data Out
12 Sig' Valid Out
8 Signal Ground
1 Shield / Prot'
ground
P300 Modem Installation and Operating Handbook
RS422 Circuit
Name Number
SD 103
RS 105
RT 115 17
RD 104
RR 109
SG 102
PG 101
25 pin 37 pin
A B A B
2 14 4 22
4 19 7 25
9 8 26
3 16 6 24
8 10 13 31
7 19, 20, 21
1 1
Electrical
Levels
RS422
RS422
RS422
RS422
RS422
Ground
Screen
Page 162