Canoga Perkins 2240 User Manual page 47

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 combina-
tion more "DTE-like" in tail circuit applications at the clock source end (refer to
Section 2.2.6). 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 (refer to Section 2.2.6). 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).
The control signal outputs are unbalanced drivers (conforming to the RS-423
Standard). The B-leads of any differential control signal outputs are tied to signal
ground to comply with RS-422.
None of the control leads interact with the data transmission. They are provided
in order to comply with a variety of DTE interface requirements. Most of the
control leads are actually end-to-end signal channels which can be used for any
purpose as long as it conforms to the RS-449 interface standards.
Three 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 two end-to-
end control lead pairs are listed below with the input signal listed first:
TR to IC
NS to SQ
DM and TM are local status leads and follow the functions described in RS-449.
Data Mode (DM) typically indicates that the modem is ready to handle transmit
data. During loopbacks, the behavior of this signal is dependent on the position of
the DM jumper (see description of DM jumper).
2240 Fiber Optic Modem
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