SN54AS877, SN74AS877
8-BIT UNIVERSAL TRANSCEIVER PORT CONTROLLERS

SDAS234 - D2661, DECEMBER 1982 - REVISED AUGUST 1985

features

• Package Options Include Plastic Small Outline Packages, Both Plastic and Ceramic Chip Carriers, and Standard Plastic and Ceramic 300-mil DIPs
• Buffered 3-State Outputs Drive Bus Lines Directly
• Cascaded to n-Bits
• Eight Selectable Transceiver/Port Functions:
  A to B or B to A
  Register to A or Register to B
  Shifted to A or Shifted to B
  Off-Line Shifts (A and B Ports in
  High-Impedance State)
  Register Clear
• Particularly Suitable for Use in Signature Analysis Circuitry
• Serial Register Provides:
  Parallel Storage of Either A or B Input
  Data
  Serial Transmission of Data from Either
  A or B Port
• Dependable Texas Instruments Quality and Reliability

description

The 'AS877 features two 8-bit I/O ports (A1-A8 and B1-B8), an 8-bit parallel-load, serial-in, parallel-out shift register, and control logic. With these features, this device is capable of performing eight selectable transceiver or port functions, depending on the state of the three select lines S0, S1, and S2. These functions include: transferring data from port A to port B or vice versa (i.e., the transceiver function), transferring data from the register to either port,

serial shifting data to either port, performing off-line shifts (with A and B ports in high-impedance state), and clearing the register. Synchronous parallel loading of the internal register can be accomplished from either port on the positive transition of the clock while serially shifting data in via the SERIN input. The 'AS877 is ideally suited for applications needing signature-analysis circuitry to enhance system verification and/or fault analysis. All serial data is shifted right. All outputs are buffer-type outputs designed specifically to drive bus lines directly and all are 3-state except for Q8, which is a totem-pole output.

The SN54AS877 is characterized for operation over the full military temperature range of -55°C to 125°C. The SN74AS877 is characterized for operation from 0°C to 70°C.

n = level Of Q_n(n = 1, 2 . . . 8) established on most recent transition of CLK. Q1 thru Q8 are the shift register outputs; only Q8 is available externally. The double
inversions that take place as data travels from port to port are ignored in this table.