MCM69C432 Datasheet, PDF (16/20 Pages) Motorola, Inc – 16K x 64 CAM

TEST ACCESS PORT DESCRIPTION
INSTRUCTION SET
A five pin IEEE Standard 1149.1 Test Port (JTAG) is in-
cluded on this device. When the TAP (Test Access Port) con-
troller is in the SHIFT–IR state, the instruction register is
placed between TDI and TDO. In this state, the desired
instruction would be serially loaded through the TDI input.
TRST resets the TAP controller to the test–logic reset state.
The TAP instruction set for this device are as follows.
STANDARD INSTRUCTIONS
Instruction
Code
(Binary)
Description
BYPASS
1111* Bypass instruction
SAMPLE/PRELOAD
0010
Sample and/or preload
instruction
EXTEST
0000 Extest instruction
HIGHZ
1001
High–Z all output pins while
bypass register is between
TDI and TDO
CLAMP
1100
* Default state at power–up.
Clamp output pins while
bypass register is between
TDI and TDO
SAMPLE/PRELOAD TAP INSTRUCTION
The SAMPLE/PRELOAD TAP instruction is used to allow
scanning of the boundary–scan register without causing in-
terference to the normal operation of the chip logic. The
62–bit boundary–scan register contains bits for all device
signal and clock pins and associated control signals. This
register is accessible when the SAMPLE/PRELOAD TAP
instruction is loaded into the TAP instruction register in the
SHIFT–IR state. When the TAP controller is then moved to
the SHIFT–DR state, the boundary–scan register is placed
between TDI and TDO. This scan register can then be used
prior to the EXTEST instruction to preload the output pins
with desired values so that these pins will drive the desired
state when the EXTEST instruction is loaded. As data is writ-
ten into TDI, data also streams out TDO which can be used
to pre–sample the inputs and outputs.
SAMPLE/PRELOAD would also be used prior to the
CLAMP instruction to preload the values on the output pins
that will be driven out when the CLAMP instruction is loaded.
EXTEST TAP INSTRUCTION
The EXTEST instruction is intended to be used in con-
junction with the SAMPLE/PRELOAD instruction to assist in
testing board level connectivity. Normally, the SAMPLE/
PRELOAD instruction would be used to preload all output
pins. The EXTEST instruction would then be loaded. During
EXTEST, the boundary–scan register is placed between TDI
and TDO in the SHIFT–DR state of the TAP controller. Once
the EXTEST instruction is loaded, the TAP controller would
then be moved to the run–test/idle state. In this state, one
cycle of TCK would cause the preloaded data on the output
pins to be driven while the values on the input pins would be
sampled. Note the TCK, not the clock pin (CLK), is used as
the clock input while CLK is only sampled during EXTEST.
After one clock cycle of TCK, the TAP controller would then
be moved to the SHIFT–DR state where the sampled values
would be shifted out of TDO (and new values would be
shifted in TDI). These values would normally be compared to
expected values to test for board connectivity.
MCM69C432
16
MOTOROLA FAST SRAM