Paradise P300 User Manual
Page 173
P300H
P300 Series Modem Installation and Operating Handbook
Page 173
P1440 IN X.21 MODE
The P300 Series 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:
Min
Signal
RS422
Circuit
Electrical
Req
Description
Name
Number
Levels
X.21 DCE
(15 pin D female)
25 pin
37 pin
Name
A
B
A
B
A
B
DATA CIRCUIT TOWARDS MODEM (TX)
U
T
2
9
Data In
SD
103
2
14
4
22
RS422
C
3
10
Sig’ Valid In
RS
105
4
19
7
25
RS422
DATA CIRCUIT FROM MODEM (RX)
U
S
6
13
Clock Out
RT
115
17
9
8
26
RS422
U
R
4
11
Data Out
RD
104
3
16
6
24
RS422
I
5
12
Sig’ Valid Out
RR
109
8
10
13
31
RS422
COMMON LINES
U
Sig gnd
8
Signal Ground
SG
102
7
19, 20, 21
Ground
U
Prot gnd
1
Shield / Prot’
PG
101
1
1
Screen
ground
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
.