GS881E18 View Datasheet(PDF) - Giga Semiconductor
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GS881E18 Datasheet PDF : 34 Pages
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Preliminary
GS881E18/36T-11/11.5/100/80/66
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.
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
TDI Test Data In In 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 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 are serial shift registers that capture serial input data on the rising edge of TCK and
push 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 RAMs JTAG Port to another device in the scan chain with as little delay as possible.
Boundary Scan Register
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
Register, under the control of the TAP Controller, is loaded with the contents of the RAMs I/O ring when the controller is in
Capture-DR state and then is placed between the TDI and TDO pins when the controller is moved to Shift-DR state. Two TAP
instructions can be used to activate the Boundary Scan Register.
Rev: 1.10 9/2000
24/34
© 2000, Giga Semiconductor, Inc.
Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com.
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