CY7C1354A/GVT71256ZC36
CY7C1356A/GVT71512ZC18
Document #: 38-05161 Rev. *B
Page 11 of 31
Identification (ID) Register
The ID Register is a 32-bit register that is loaded with a device
and vendor specific 32-bit code when the controller is put in
Capture-DR state with the IDCODE command loaded in the
instruction register. The register is then placed between the
TDI and TDO pins when the controller is moved into Shift-DR
state. Bit 0 in the register is the LSB and the first to reach TDO
when shifting begins. The code is loaded from a 32-bit on-chip
ROM. It describes various attributes of the device as described
in the Identification Register Definitions table.
TAP Controller Instruction Set
Overview
There are two classes of instructions defined in the IEEE
Standard 1149.1-1990; the standard (public) instructions and
device specific (private) instructions. Some public instructions
are mandatory for IEEE 1149.1 compliance. Optional public
instructions must be implemented in prescribed ways.
Although the TAP controller in this device follows the IEEE
1149.1 conventions, it is not IEEE 1149.1 compliant because
some of the mandatory instructions are not fully implemented.
The TAP on this device may be used to monitor all input and
I/O pads, but can not be used to load address, data, or control
signals into the device or to preload the I/O buffers. In other
words, the device will not perform IEEE 1149.1 EXTEST,
INTEST, or the preload portion of the SAMPLE/PRELOAD
command.
When the TAP controller is placed in Capture-IR state, the two
least significant bits of the instruction register are loaded with
01. When the controller is moved to the Shift-IR state the
instruction is serially loaded through the TDI input (while the
previous contents are shifted out at TDO). For all instructions,
the TAP executes newly loaded instructions only when the
controller is moved to Update-IR state. The TAP instruction
sets for this device are listed in the following tables.
EXTEST
EXTEST is an IEEE 1149.1 mandatory public instruction. It is
to be executed whenever the instruction register is loaded with
all 0s. EXTEST is not implemented in this device.
The TAP controller does recognize an all-0 instruction. When
an EXTEST instruction is loaded into the instruction register,
the device responds as if a SAMPLE/PRELOAD instruction
has been loaded. There is one difference between two instruc-
tions. Unlike SAMPLE/PRELOAD instruction, EXTEST places
the device outputs in a High-Z state.
IDCODE
The IDCODE instruction causes a vendor-specific, 32-bit code
to be loaded into the ID register when the controller is in
Capture-DR mode and places the ID register between the TDI
and TDO pins in Shift-DR mode. The IDCODE instruction is
the default instruction loaded in the instruction upon power-up
and at any time the TAP controller is placed in the test-logic
reset state.
SAMPLE-Z
If the High-Z instruction is loaded in the instruction register, all
output pins are forced to a High-Z state and the boundary scan
register is connected between TDI and TDO pins when the
TAP controller is in a Shift-DR state.
SAMPLE/PRELOAD
SAMPLE/PRELOAD is an IEEE 1149.1 mandatory instruction.
The PRELOAD portion of the command is not implemented in
this device, so the device TAP controller is not fully IEEE
1149.1-compliant.
When the SAMPLE/PRELOAD instruction is loaded in the
instruction register and the TAP controller is in the Capture-DR
state, a snap shot of the data in the device’s input and I/O
buffers is loaded into the boundary scan register. Because the
device system clock(s) are independent from the TAP clock
(TCK), it is possible for the TAP to attempt to capture the input
and I/O ring contents while the buffers are in transition (i.e., in
a metastable state). Although allowing the TAP to sample
metastable inputs will not harm the device, repeatable results
can not be expected. To guarantee that the boundary scan
register will capture the correct value of a signal, the device
input signals must be stabilized long enough to meet the TAP
controller’s capture set-up plus hold time (tCS plus tCH). The
device clock input(s) need not be paused for any other TAP
operation except capturing the input and I/O ring contents into
the boundary scan register.
Moving the controller to Shift-DR state then places the
boundary scan register between the TDI and TDO pins.
Because the PRELOAD portion of the command is not imple-
mented in this device, moving the controller to the Update-DR
state with the SAMPLE/PRELOAD instruction loaded in the
instruction register has the same effect as the Pause-DR
command.
BYPASS
When the BYPASS instruction is loaded in the instruction
register and the TAP controller is in the Shift-DR state, the
bypass register is placed between TDI and TDO. This allows
the board level scan path to be shortened to facilitate testing
of other devices in the scan path.
Reserved
Do not use these instructions. They are reserved for future
use.
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