Paradise P300 specifications P1440 in X.21 Mode, DCE Operation, Clocking Important

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	X.21 DCE			Signal
	(15 pin D female)
Req				Description
	Name	A	B
DATA CIRCUIT TOWARDS MODEM (TX)

RS422	Circuit	25 pin		37 pin		Electrical
Name	Number					Levels
		A	B	A	B

	T	2	9	Data In
	C	3	10	Sig’ Valid In
DATA CIRCUIT FROM MODEM (RX)
	S	6	13	Clock Out
	R	4	11	Data Out
	I	5	12	Sig’ Valid Out
COMMON LINES
	Sig gnd	8		Signal Ground
U	Prot gnd	1		Shield / Prot’
				ground

Clocking: IMPORTANT

SD

RS

RT

RD

RR

SG

PG

103

105

115

104

109

102

101

2		14	4		22
4		19	7		25
17		9	8		26
3		16	6		24
8		10	13		31
	7		19, 20, 21
	1			1

RS422

RS422

RS422

RS422

RS422

Ground

Screen

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 P300 Series Modem Installation and Operating Handbook Page 173