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SP504 Datasheet(PDF) 29 Page - Exar Corporation |
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SP504 Datasheet(HTML) 29 Page - Exar Corporation |
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29 / 32 page  Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 50-668-707 • www.exar.com SP504_02_2708 29 Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 50-668-707 • www.exar.com SP504_02_2708 Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 50-668-707 • www.exar.com SP504_02_2708 ADDITIONAL TRANSCEIVERS WITH THE SP504 Serial ports usually can have two data sig- nals (SD, RD), three clock signals (TT, ST, RT), and at least eight control signals (CS, RS, etc.). EIA-RS-449 contains twenty six signal types for a DB-37 connector. A DB- 37 serial port design may require thirteen drivers and fourteen receivers. Although many applications do not use all these signals, some applications may need to support extra functions such as diagnostics. The SP504 supports enough transceivers for the primary channels of data, clock and control signals. Configuring LL, RL and TM would require two additional drivers and one receiver if designing for a DTE (one driver and two receivers for a DCE). A programmable transceiver such as the SP332 is a convenient solution in a design thatrequiresextrasingleendedordifferential drivers/receivers.As shown in Figure 28, the SP332 can be configured to four different variations. The SP332 in Figure 29 is configured for two single-ended drivers and one diffferential receiver. For a DTE design, the two drivers are used for LL and RL signals and the receiver is used for the TM signal. This configuration was selected because the two RS-232 drivers can be used for RS-423 by connectingazenerclampingdiodetoground on the two driver outputs. The diodes will limit the voltage swing on the outputs so that the V OC = ±4V to ±6V adheres to the RS-423 specification. The differential receiver can be easily configured to RS-423 by ground- ing the non-inverting input. The receiver will adhere to the RS-423 specifications. CIRCUIT CIRCUIT NAME CIRCUIT CIRCUIT MNEMONIC DIRECTION TYPE SG SIGNAL GROUND -------------- SC SEND COMMON TO DCE RC RECEIVE COMMON FROM DCE IS TERMINAL IN SERVICE TO DCE IC INCOMING CALL FROM DCE TR TERMINAL READY TO DCE DM DATA MODE FROM DCE SD SEND DATA TO DCE RD RECEIVE DATA FROM DCE TT TERMINAL TIMING TO DCE ST SEND TIMING FROM DCE RT RECEIVE TIMING FROM DCE RS REQUEST TO SEND TO DCE CS CLEAR TO SEND FROM DCE RR RECEIVER READY FROM DCE SQ SIGNAL QUALITY FROM DCE NS NEW SIGNAL TO DCE SF SELECT FREQUENCY TO DCE SR SIGNAL RATE SELECTOR TO DCE SI SIGNAL RATE INDICATOR FROM DCE SSD SECONDARY SEND DATA TO DCE SRD SECONDARY RD FROM DCE SRS SECONDARY RS TO DCE SCS SECONDARY CS FROM DCE SRR SECONDARY RR FROM DCE LL LOCAL LOOPBACK TO DCE RL REMOTE LOOPBACK TO DCE TM TEST MODE FROM DCE SS SELECT STANDBY TO DCE SB STANDBY INDICATOR FROM DCE COMMON CONTROL DATA TIMING CONTROL DATA CONTROL CONTROL CONTROL RS-449 Interchange Circuits Table SEL A 0 0 SEL B 0 0 LOOPBACK SHUTDOWN 0 0 0 0 Figure 28. Mode selection for the SP332 |
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