SN54ABTH18504A, SN54ABTH182504A, SN74ABTH18504A, SN74ABTH182504A

SCAN TEST DEVICES WITH

20-BIT UNIVERSAL BUS TRANSCEIVERS

SCBS165C – AUGUST 1993 – REVISED JULY 1996

2

POST OFFICE BOX 655303

18 19

48

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A4

A5

A6

GND

A7

A8

A9

A10

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A12

A13

GND

A14

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A16

B5

B6

B7

GND

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B9

B10

B11

B12

B13

B14

GND

B15

B16

B17

SN74ABTH18504A, SN74ABTH182504A . . . PM PACKAGE

(TOP VIEW)

description

The ’ABTH18504A and ’ABTH182504A scan test devices with 20-bit universal bus transceivers are members

of the Texas Instruments SCOPE

™ testability integrated-circuit family. This family of devices supports IEEE

Standard 1149.1-1990 boundary scan to facilitate testing of complex circuit-board assemblies. Scan access to

the test circuitry is accomplished via the 4-wire test access port (TAP) interface.

In the normal mode, these devices are 20-bit universal bus transceivers that combine D-type latches and D-type

flip-flops to allow data flow in transparent, latched, or clocked modes. The test circuitry can be activated by the

TAP to take snapshot samples of the data appearing at the device pins or to perform a self test on the

boundary-test cells. Activating the TAP in the normal mode does not affect the functional operation of the

SCOPE

™ universal bus transceivers.

Data flow in each direction is controlled by output-enable (OEAB and OEBA), latch-enable (LEAB and LEBA),

clock-enable (CLKENAB and CLKENBA), and clock (CLKAB and CLKBA) inputs. For A-to-B data flow, the

device operates in the transparent mode when LEAB is high. When LEAB is low, the A-bus data is latched while

CLKENAB is high and/or CLKAB is held at a static low or high logic level. Otherwise, if LEAB is low and

CLKENAB is low, A-bus data is stored on a low-to-high transition of CLKAB. When OEAB is low, the B outputs

are active. When OEAB is high, the B outputs are in the high-impedance state. B-to-A data flow is similar to

A-to-B data flow, but uses the OEBA, LEBA, CLKENBA, and CLKBA inputs.

In the test mode, the normal operation of the SCOPE

™ universal bus transceivers is inhibited, and the test

circuitry is enabled to observe and control the I/O boundary of the device. When enabled, the test circuitry

performs boundary-scan test operations according to the protocol described in IEEE Standard 1149.1-1990.