DS2155 datasheet(199/238 Pages) DALLAS

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DS2155

199 of 238

34.

JTAG BOUNDARY SCAN ARCHITECTURE AND TEST ACCESS PORT

34.1 Description

The DS2155 IEEE 1149.1 design supports the standard instruction codes SAMPLE/PRELOAD,

BYPASS, and EXTEST. Optional public instructions included are HIGH-Z, CLAMP, and IDCODE

(Figure 34-1.). The DS2155 contains the following features as required by IEEE 1149.1 standard test

access port (TAP) and boundary scan architecture.

Test Access Port

TAP Controller

Instruction Register

Bypass Register

Boundary Scan Register

Device Identification Register

The DS2155 is pin-compatible with the DS2152, DS21x52 (T1) and DS2154, DS21x54 (E1) SCT

families. The JTAG feature uses pins that had no function in the DS2152 and DS2154. Details about

boundary scan architecture and the TAP are in IEEE 1149.1-1990, IEEE 1149.1a-1993, and IEEE

1149.1b-1994. NOTE: JTAG functionality is production tested at 25C only.

The TAP contains the necessary interface pins JTRST, JTCLK, JTMS, JTDI, and JTDO. See the pin

descriptions in Section 4 for details.

Figure 34-1. JTAG Functional Block Diagram

BOUNDARY SCAN

IDENTIFICATION

BYPASS

INSTRUCTION

JTDI

JTMS

JTCLK

JTRST

JTDO

TEST ACCESS PORT

CONTROLLER

MUX

10kΩ

SELECT

OUTPUT ENABLE

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