AT697F datasheet(67/155 Pages) ATMEL

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AT697F ADVANCE INFORMATION

7703C–AERO–6/09

JTAG Interface

Overview

The AT697 implements a standard interface compliant with the IEEE 1149.1 JTAG specification.

This interface can be used for PCB testing using the JTAG boundary-scan capability.

The JTAG interface is accessed through five dedicated pins. In JTAG terminology, these pins

constitute the Test Access Port (TAP).

The following table summarizes the TAP pins and there function at JTAG level.

Table 24.

Name

Type

Description

TCK

Test Clock

Input

Used to clock serial data boundary into scan latches and control

sequence of the test state machine. TCK can be asynchronous

with CLK

TMS

Test Mode select

Input

Primary control signal for the state machine. Synchronous with

TCK. A sequence of values on TMS adjusts the current state of

the TAP.

TDI

Test Data Input

Input

Serial input data to the boundary scan latches. Synchronous

with TCK

TDO

Test Data Output

Output

Serial output data from the boundary scan latches.

Synchronous with TCK

TRST

Test Reset

Input

Resets the test state machine. can be asynchronous with TCK

TAP Pins

For more details, please refer to the ‘IEEE Standard Test Access Port and Boundary Scan’

specification.

Any AT697 based system will contain several JTAG compatible chips. These are connected

using the minimum (single TMS signal) configuration. This configuration contains three broad-

cast signals (TMS, TCK, and TRST,) which are fed from the JTAG master to all JTAG slaves in

parallel, and a serial path formed by a daisy-chain connection of the serial test data pins (TDI

and TDO) of all slaves.

The TAP supports a BYPASS instruction which places a minimum shift path (1 bit) between the

chip’s TDI and TDO pins. This allows efficient access to any single chip in the daisy-chain with-

out board-level multiplexing.

Figure 42. JTAG Serial connection using 1 TMS Signal

TDI

TDO

TMS TCK

TRST

TDI

TDO

TMS TCK

TRST

TDI

TDO

TMS TCK

TRST

TDI

TDO

TMS TCK

TRST

TDI

TMS

TCK

TRST

TDO

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