SN74BCT979
9-BIT REGISTERED BTL TRANSCEIVER
WITH PARITY GENERATOR/CHECKER

SCBS115A - OCTOBER 1990 - REVISED NOVEMBER 1993

features

• BiCMOS Design Significantly Reduces I_CCZ
• ESD Protection Exceeds 2000 V Per MIL-STD-883C, Method 3015; Exceeds 200 V Using Machine Model (C = 200 pF, R = 0)
• Support IEEE BTL Standard 1194.1-1991
• Open-Collector B Port Drives Load Impedances as Low as 10
• BTL Logic Level 1-V Bus Swing Reduces Power Consumption
• Latchable Transceiver With Output Sink of 24 mA at the A Bus and 100 mA at the
  B Bus
• Option to Generate and Check Parity or Feed-Through Data/Parity in Directions
  A to B or B to A
• Independent Latch Enables for A-to-B and B-to-A Directions
• Select Pin for ODD Parity
• and Output Pins for Parity Checking
• Ability to Simultaneously Generate and Check Parity
• Packaged in 300-mil Plastic Shrink Small-Outline (DL) Package

description

The SN74BCT979 is a 9-bit to 9-bit parity transceiver with transparent latches. The device can operate as a feed-through transceiver, or it can generate/check parity from the 8-bit data bus in either direction. It has a guaranteed current-sinking capability of 24 mA at the A bus and 100 mA at the open-collector B bus.

The SN74BCT979 features independent latch-enable (LEAB, LEBA) inputs for the A-to-B direction and the B-to-A direction, an ODD input to select odd or even parity, and separate error-signal (, ) outputs for checking parity.

When communication between buses occurs, parity is generated and passed on to either bus as APARO or BPAR. Error detection of the parity generated from AI1-AI8 and B1-B8 can be checked by and, providing LEAB and LEBA are high and the mode select () is low. If is high, the communication between buses is in a feed-through mode where parity is still generated and checked as and.

The SN74BCT979 features open-collector driver outputs (B port) with a series Schottky diode to reduce capacitive loading to the bus. By using a 2-V pullup on the bus, the output signal swing will be approximately 1 V, which reduces the power necessary to drive the bus load capacitance. The driver outputs are capable of driving an equivalent dc load of as low as 10 .

The transceiver has a precision threshold set by an internal bandgap reference to give accurate input thresholds over V_CC and temperature variations.

This transceiver is compatible with backplane transceiver logic (BTL) technology at significantly reduced power dissipation per channel.

The SN74BCT979 is characterized for operation from 0°C to 70°C.