
Rev:  1.01  11/2000
Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com.
27/39
 2000, Giga Semiconductor, Inc.
Preliminary
GS8152Z18/36/72B-225/200/180/166/150/133
JTAG Port Operation
Overview
The JTAG Port on this RAM operates in a manner consistent with IEEE Standard 1149.1-1990, a serial boundary scan interface standard 
(commonly referred to as JTAG), but does not implement all of the functions required for 1149.1 compliance. Unlike JTAG implementations that 
have been common among SRAM vendors for the last several years, this implementation does offer a form of EXTEST, known as Clock Assisted 
EXTEST, reducing or eliminating the “hand coding” that has been required to overcome the test program compiler errors caused by previous non-
compliant implementations. The JTAG Port interfaces with conventional 2.5  V CMOS logic level signaling.
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 Port unused, TCK, TDI, and TMS may 
be left floating or tied to either V
DD
 or V
SS
. TDO should be left unconnected. 
JTAG Port Registers
Overview
The various JTAG registers, refered to as Test Access Port orTAP 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.
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.