Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com.

Rev: 1.02a 11/2012

21/30

© 2011, GSI Technology

GS8342D06/11/20/38BD-550/500/450/400/350

JTAG Port Operation

Overview

The JTAG Port on this RAM operates in a manner that is compliant with IEEE Standard 1149.1-1990, a serial boundary scan

Disabling the JTAG Port

It is possible to use this device without utilizing the JTAG port. The port is reset at power-up and will remain inactive unless

clocked. TCK, TDI, and TMS are designed with internal pull-up circuits.To assure normal operation of the RAM with the JTAG

JTAG Pin Descriptions

Pin

Pin Name

I/O

Description

TCK

Test Clock

In

Clocks all TAP events. All inputs are captured on the rising edge of TCK and all outputs propagate from the

falling edge of TCK.

TMS

Test Mode Select

In

The TMS input is sampled on the rising edge of TCK. This is the command input for the TAP controller state

machine. An undriven TMS input will produce the same result as a logic one input level.

TDI

Test Data In

In

The TDI input is sampled on the rising edge of TCK. This is the input side of the serial registers placed

between TDI and TDO. The register placed between TDI and TDO is determined by the state of the TAP

Controller state machine and the instruction that is currently loaded in the TAP Instruction Register (refer to

the TAP Controller State Diagram). An undriven TDI pin will produce the same result as a logic one input

level.

TDO

Test Data Out

Out

Output that is active depending on the state of the TAP state machine. Output changes in response to the

falling edge of TCK. This is the output side of the serial registers placed between TDI and TDO.

Note:

This device does not have a TRST (TAP Reset) pin. TRST is optional in IEEE 1149.1. The Test-Logic-Reset state is entered while TMS is

held high for five rising edges of TCK. The TAP Controller is also reset automaticly at power-up.

JTAG Port Registers

Overview

The various JTAG registers, refered to as Test Access Port or TAP Registers, are selected (one at a time) via the sequences of 1s

and 0s applied to TMS as TCK is strobed. Each of the TAP Registers is a serial shift register that captures serial input data on the

rising edge of TCK and pushes serial data out on the next falling edge of TCK. When a register is selected, it is placed between the

TDI and TDO pins.

Instruction Register

The Instruction Register holds the instructions that are executed by the TAP controller when it is moved into the Run, Test/Idle, or

the various data register states. Instructions are 3 bits long. The Instruction Register can be loaded when it is placed between the

TDI and TDO pins. The Instruction Register is automatically preloaded with the IDCODE instruction at power-up or whenever the

controller is placed in Test-Logic-Reset state.

Bypass Register

The Bypass Register is a single bit register that can be placed between TDI and TDO. It allows serial test data to be passed through

the RAM’s JTAG Port to another device in the scan chain with as little delay as possible.

Boundary Scan Register

The Boundary Scan Register is a collection of flip flops that can be preset by the logic level found on the RAM’s input or I/O pins.

The flip flops are then daisy chained together so the levels found can be shifted serially out of the JTAG Port’s TDO pin. The

Boundary Scan Register also includes a number of place holder flip flops (always set to a logic 1). The relationship between the

device pins and the bits in the Boundary Scan Register is described in the Scan Order Table following. The Boundary Scan