CANOGA PERKINS 2240 Fiber Optic Modem User Manual

Page 56

2240 Fiber Optic Modem User Manual

Chapter 4 Data Interfaces

Multi-Channel Interfaces

The SD, RD, ST, RT and TT pins carry the primary data and clock signals (conforming to the RS-
449 and RS-422 standards). In addition, an extra clock signal input (conforming to RS-422) is
provided to make the 2240/-422 combination more "DTE-like" in tail circuit applications at the
clock source end. The remainder of the pins are either ground references or control signals.
Send Data (SD) and Receive Data (RD) are the data input and output signals for the modem,
respectively.

Send Timing (ST) is the modem’s transmit clock reference output that is used for the internal and
slave clock modes. Receive Timing (RT) is the clock signal for the receive data unless the 2240's
main PCBA W26 (XTCLK) jumper is ON, in which case the Extra Clock input signal is used to
shift receive data out from the 2240. Terminal Timing (TT) is the transmit clock signal used in
either of the External clock modes or when the main board internal CLK/EXT switch is set to EXT
(refer to section 3.7).

NOTE: The extra clock signal is an enhancement added to -422 interfaces. The -

422 interfaces with this capability can be identified by their lack of the
W16/W15 BAL_CTRL jumper. The W16/W15 jumper was never described
in the manual, so do not try to find a reference to it in the manual.

Two end-to-end control leads are provided as part of this interface. An input to RS (Request to
Send) is transmitted to the RR (Receiver Ready) output at the other end of the link (see
description of RS-Bias jumper and RR jumper). CS (Clear to Send) follows RS locally but is
delayed approximately 1 millisecond when RS turns ON (see description of CS-Gate jumper).
The other end-to-end control lead pair is listed below with the input signal listed first:

•

TR to IC

This path, in conjunction with crossover cables at the DCE-DCE end, can be used to implement
incoming call handshaking (see Figure 3-2).

Local Loopback (LL) and Remote Loopback (RL) are loopback control leads and perform the
same functions as the 2240 front panel LOOP switch LOC and REM positions. LL and RL are

12/30

terminal ready

to modem

13/31

receiver ready

from modem

remote loopback

to modem

incoming call

from modem

17/35

terminal timing

to modem

test mode

from modem

signal ground -

receive common -

send common

to modem

2/36

N/A

extra clock for
receive data

to modem

Table 4-9. RS-449 Pinouts for Model MC1 (Continued)

Pin

Number

A/B

RS-449 Pin

Name (abbrev)

(full name)

Direction