Cypress NoBL CY7C1471V25 User Manual download pdf (Page 14)

CY7C1471V25

CY7C1473V25

CY7C1475V25

Document #: 38-05287 Rev. *I Page 14 of 32

TAP Registers

Registers are connected between the TDI and TDO balls and

enable data to be scanned into and out of the SRAM test

circuitry. Only one register can be selected at a time through

the instruction register. Data is serially loaded into the TDI ball

on the rising edge of TCK. Data is output on the TDO ball on

the falling edge of TCK.

Instruction Register

Three-bit instructions can be serially loaded into the instruction

TDI and TDO balls as shown in the “TAP Controller Block

Diagram” on page 13. During power up, the instruction register

is loaded with the IDCODE instruction. It is also loaded with

the IDCODE instruction if the controller is placed in a reset

state as described in the previous section.

When the TAP controller is in the Capture-IR state, the two

least significant bits are loaded with a binary ‘01’ pattern to

enable fault isolation of the board-level serial test data path.

Bypass Register

To save time when serially shifting data through registers, it is

sometimes advantageous to skip certain chips. The bypass

TDI and TDO balls. This allows data to be shifted through the

SRAM with minimal delay. The bypass register is set LOW

) when the BYPASS instruction is executed.

Boundary Scan Register

The boundary scan register is connected to all the input and

bidirectional balls on the SRAM.

The boundary scan register is loaded with the contents of the

RAM IO ring when the TAP controller is in the Capture-DR

state and is then placed between the TDI and TDO balls when

the controller is moved to the Shift-DR state. The EXTEST,

SAMPLE/PRELOAD and SAMPLE Z instructions can be used

to capture the contents of the IO ring.

The Boundary Scan Order tables show the order in which the

bits are connected. Each bit corresponds to one of the bumps

on the SRAM package. The MSB of the register is connected

to TDI and the LSB is connected to TDO.

Identification (ID) Register

The ID register is loaded with a vendor-specific, 32-bit code

during the Capture-DR state when the IDCODE command is

loaded in the instruction register. The IDCODE is hardwired

into the SRAM and can be shifted out when the TAP controller

is in the Shift-DR state. The ID register has a vendor code and

other information described in “Identification Register Defini-

tions” on page 17.

TAP Instruction Set

Overview

Eight different instructions are possible with the three-bit

instruction register. All combinations are listed in “Identification

Codes” on page 18. Three of these instructions are listed as

RESERVED and must not be used. The other five instructions

are described in this section in detail.

The TAP controller used in this SRAM is not fully compliant to

the 1149.1 convention because some of the mandatory 1149.1

instructions are not fully implemented.

The TAP controller cannot be used to load address data or

control signals into the SRAM and cannot preload the IO

buffers. The SRAM does not implement the 1149.1 commands

EXTEST or INTEST or the PRELOAD portion of

SAMPLE/PRELOAD; rather, it performs a capture of the IO

ring when these instructions are executed.

Instructions are loaded into the TAP controller during the

Shift-IR state when the instruction register is placed between

TDI and TDO. During this state, instructions are shifted

through the instruction register through the TDI and TDO balls.

To execute the instruction after it is shifted in, the TAP

controller needs to be moved into the Update-IR state.

EXTEST

EXTEST is a mandatory 1149.1 instruction which is to be

executed whenever the instruction register is loaded with all

0s. EXTEST is not implemented in this SRAM TAP controller,

and therefore this device is not compliant to 1149.1. The TAP

controller does recognize an all-0 instruction.

When an EXTEST instruction is loaded into the instruction

instruction has been loaded. There is one difference between

the two instructions. Unlike the SAMPLE/PRELOAD

instruction, EXTEST places the SRAM outputs in a High-Z

state.

IDCODE

The IDCODE instruction causes a vendor-specific, 32-bit code

to be loaded into the instruction register. It also places the

instruction register between the TDI and TDO balls and

enables the IDCODE to be shifted out of the device when the

TAP controller enters the Shift-DR state.

The IDCODE instruction is loaded into the instruction register

during power up or whenever the TAP controller is in a test

logic reset state.

SAMPLE Z

The SAMPLE Z instruction causes the boundary scan register

to be connected between the TDI and TDO balls when the TAP

controller is in a Shift-DR state. It also places all SRAM outputs

into a High-Z state.

SAMPLE/PRELOAD

SAMPLE/PRELOAD is a 1149.1 mandatory instruction. The

PRELOAD portion of this instruction is not implemented, so

the device TAP controller is not fully 1149.1 compliant.

When the SAMPLE/PRELOAD instruction is loaded into the

instruction register and the TAP controller is in the Capture-DR

state, a snapshot of data on the inputs and bidirectional balls

is captured in the boundary scan register.

The user must be aware that the TAP controller clock can only

operate at a frequency up to 20 MHz, while the SRAM clock

operates more than an order of magnitude faster. Because

there is a large difference in the clock frequencies, it is

possible that during the Capture-DR state, an input or output

may undergo a transition. The TAP may then try to capture a

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Cypress NoBL CY7C1471V25 User Manual Page 14

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