Paradise P300 User Manual
Page 174
P300H
P300 Series Modem Installation and Operating Handbook
Page 174
X.21 DTE OPERATION
This only has 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 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 DTE
(15 pin D male)
25 pin
37 pin
Name
A
B
A
B
A
B
DATA CIRCUIT TOWARDS MODEM (TX)
U
S
6
13
Clock In
TT
113
24
11
17
35
RS422
U
R
4
11
Data In
SD
103
2
14
4
22
RS422
I
5
12
Sig’ Valid In
RS
105
4
19
7
25
RS422
DATA CIRCUIT FROM MODEM (RX)
U
T
2
9
Data Out
RD
104
3
16
6
24
RS422
C
3
10
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 Tx Clocking menu should
be set take the single clock from the terrestrial by selecting
Tx Clock In.
The Rx Clock 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.
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 (I) 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 (I) by selecting
Change
,
Tx
,
Modulator
,
Carrier
,
RTS-
Controlled
.