SN54ACT8997, SN74ACT8997

SCAN-PATH LINKERS WITH 4-BIT IDENTIFICATION BUSES

SCAN-CONTROLLED IEEE STD 1149.1 (JTAG) TAP CONCATENATORS

SCAS157D – APRIL 1990 – REVISED DECEMBER 1996

3

POST OFFICE BOX 655303

functional block description

The ’ACT8997 is intended to link secondary scan paths for inclusion in a primary scan path. Any combination

of the four secondary scan paths can be linked, or the device can be bypassed entirely.

The least-significant bit (LSB) of any value scanned into any register of the device is the first bit shifted in

(nearest to TDO). The most-significant bit (MSB) is the last bit shifted in (nearest to TDI).

The ’ACT8997 is divided into functional blocks as detailed below.

test port

The test port decodes the signals on TCK, TMS, and TRST to control the operation of the circuit. The test port

includes a TAP controller that issues the proper control instructions to the data registers according to the

IEEE Standard 1149.1 protocol. The TAP controller state diagram is shown in Figure 1.

instruction register

The instruction register (IR) is an 8-bit-wide serial-shift register that issues commands to the device. Data is

input to the instruction register via TDI (or one of the DTDI pins) and shifted out via TDO. All device operations

are initiated by loading the proper instruction or sequence of instructions into the IR.

data registers

Six parallel data registers are included in the ’ACT8997: bypass, control, counter, boundary-scan, ID-bus, and

select. The ID bus register is a part of the boundary-scan register. Each data register is serially loaded via TDI

or DTDI and outputs data via TDO. Table 1 summarizes the registers in the ’ACT8997.

scan-path-configuration circuit

This circuit decodes bits in the select and control registers to determine which, if any, of the secondary scan

paths are to be included in the primary scan path.

Table 1. Register Summary

REGISTER

NAME

LENGTH

(BITS)

FUNCTION

Instruction

8

Issue command information to the device

Control

10

Configuration and enable control

Counter

8

Count events on DCI, output interrupts via DCO

Select

8

Select one or more secondary scan paths

Boundary Scan

10

Capture and force test data at device periphery

ID Bus

4

Provide subsystem identification code

Bypass

1

Remove the ’ACT8997 from the scan path