CANOGA PERKINS 2240 Fiber Optic Modem - Manual (Page 46)

2240 Fiber Optic Modem User Manual Chapter 4 Data Interfaces
RS-449/422 Model 422
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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).
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).
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 OFF
position.
4.3.1 RS_BIAS Jumper
The RS_BIAS jumper controls the state that RS floats to when there is no signal driving the RS
pin. The OFF position forces this signal to the OFF (negated) state when the interface cable is
disconnected. The ON position forces it to ON (asserted).
Factory setting: OFF
4.3.2 RR Jumper
The RR Jumper determines the source of the RR output. In the CTRL position, the RR output
functions as the output for the RS input at the far end. In the CD jumper position, the RR output
will turn ON either when the modem’s fiber optic receiver is in sync (main PCBA internal switch
S1 CD/DCD = OFF and CD/SYNC = ON) or the far end RTS is ON (main PCBA internal switch
S1 CD/DCD = ON and CD/SYNC = OFF). Refer to section 2.1.3.1 for more information on the
internal switch S1 CD/DCD and CD/SYNC positions.
Factory setting: CTRL