CANOGA PERKINS 2240 Fiber Optic Modem - Manual (Page 62)

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Canoga Perkins
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 (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).
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 interface signal inputs which can be used to activate the
LOC or REM loop functions. These signals can control the loopback functions
only if the front panel switch is in the center or OFF position.