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 VDD or VSS. TDO should be left unconnected.
JTAG Pin Descriptions
Pin Name I/O
Clocks all TAP events. All inputs are captured on the rising edge of TCK and all outputs propagate
from the falling edge of TCK.
The TMS input is sampled on the rising edge of TCK. This is the command input for the TAP
TMS Test Mode Select In controller state machine. An undriven TMS input will produce the same result as a logic one input
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
Test Data In
In 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.
Output that is active depending on the state of the TAP state machine. Output changes in
Test Data Out
Out response to the falling edge of TCK. This is the output side of the serial registers placed between
TDI and TDO.
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
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.
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.
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
Register, under the control of the TAP Controller, is loaded with the contents of the RAMs I/O ring when the controller is in
Rev: 1.00b 12/2002
© 2001, Giga Semiconductor, Inc.
Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com.