| PIN | NAME | FUNCTION |
| 1 | vcc | +5V Supply Voltage (+5%). Bypass with a lUF capacitor to ground. |
| 2 | VDD | Positive Supply Generated by MXL1543. Bypass with a lUF capacitor to ground. |
| 3 | T1 llxl | Transmitter l TTL-Compatible Input |
| 4 | T211xl | Transmitter 2 TTL-Compatible Input |
| 5 | T31N | Transmitter 3 TTL-Compatible Input |
| 6 | R10UT | Receiver l CMOS Output |
| 7 | R20UT | Receiver 2 CMOS Output |
| 8 | R30UT | Receiver 3 CMOS Output |
| 9 | T411xl | Transmitter 4 TTL-Compatible Input |
| 10 | R40UT | Receiver 4 CMOS Output |
| 1 1 | MO | TTL-Compatible Mode Select Pin with Internal Pullup to VCc |
| 12 | M1 | TTL-Compatible Mode Select Pin with Internal Pullup to VCC |
| 13 | M2 | TTL-Compatible Mode Select Pin with Internal Pullup to VCC |
| 14 | DCE/DTE | TTL-Compatible Input with Internal Pullup to VCC. Logic level high selects DCE interface. |
| 15 | llxIVERT | TTL Input with Internal Pullup to VCC. INVERT = HIGH reverses action of DCE/DTE for Channel 4. |
| 16 | T40UTA/R411xIA | Transmitter Output/lnverting Receiver Input |
| 17 | R31NB | Noninverting Receiver Input |
| 18 | R31NA | Inverting Receiver Input |
| 19 | R21NB | Noninverting Receiver Input |
| 20 | R21NA | Inverting Receiver Input |
| 21 | T30UTB/R111xIB | Noninverting Transmitter Output/Noninverting Receiver Input |
| 22 | T30UTA/R11NA | Inverting Transmitter Output/lnverting Receiver Input |
| 23 | T20UTB | Noninverting Transmitter Output |
| 24 | T20UTA | Inverting Transmitter Output |
| 25 | T10UTB | Noninverting Transmitter Output |
| 26 | T10UTA | Inverting Transmitter Output |
| 27 | GND | Ground |
| 28 | VEE | Negative Supply Generated by MXL1543. Bypass with a lUF capacitor to ground. |
| | |