Cypress Semiconductor CY7C1511V18 User Manual download pdf (Page 13)

CY7C1511V18, CY7C1526V18

CY7C1513V18, CY7C1515V18

Document Number: 38-05363 Rev. *F Page 13 of 32

IEEE 1149.1 Serial Boundary Scan (JTAG)

These SRAMs incorporate a serial boundary scan Test Access

Port (TAP) in the FBGA package. This part is fully compliant with

IEEE Standard #1149.1-1900. The TAP operates using JEDEC

standard 1.8V IO logic levels.

Disabling the JTAG Feature

It is possible to operate the SRAM without using the JTAG

feature. To disable the TAP controller, TCK must be tied LOW

) to prevent clocking of the device. TDI and TMS are inter-

nally pulled up and may be unconnected. They may alternatively

be connected to V

through a pull up resistor. TDO must be left

unconnected. Upon power up, the device comes up in a reset

state, which does not interfere with the operation of the device.

Test Access Port—Test Clock

The test clock is used only with the TAP controller. All inputs are

captured on the rising edge of TCK. All outputs are driven from

the falling edge of TCK.

Test Mode Select (TMS)

The TMS input is used to give commands to the TAP controller

and is sampled on the rising edge of TCK. This pin may be left

unconnected if the TAP is not used. The pin is pulled up inter-

nally, resulting in a logic HIGH level.

Test Data-In (TDI)

The TDI pin is used to serially input information into the registers

and can be connected to the input of any of the registers. The

is loaded into the TAP instruction register. For information on

loading the instruction register, see the TAP Controller State

Diagram on page 15. TDI is internally pulled up and can be

unconnected if the TAP is unused in an application. TDI is

connected to the most significant bit (MSB) on any register.

Test Data-Out (TDO)

The TDO output pin is used to serially clock data out from the

registers. The output is active, depending upon the current state

of the TAP state machine (see Instruction Codes on page 18).

The output changes on the falling edge of TCK. TDO is

connected to the least significant bit (LSB) of any register.

Performing a TAP Reset

A Reset is performed by forcing TMS HIGH (V

) for five rising

edges of TCK. This Reset does not affect the operation of the

SRAM and can be performed while the SRAM is operating. At

power up, the TAP is reset internally to ensure that TDO comes

up in a high-Z state.

TAP Registers

Registers are connected between the TDI and TDO pins to scan

the data in and out of the SRAM test circuitry. Only one register

can be selected at a time through the instruction registers. Data

is serially loaded into the TDI pin on the rising edge of TCK. Data

is output on the TDO pin on the falling edge of TCK.

Instruction Register

Three-bit instructions can be serially loaded into the instruction

and TDO pins, as shown in TAP Controller Block Diagram on

page 16. Upon 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 allow for

fault isolation of the board level serial test path.

Bypass Register

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

sometimes advantageous to skip certain chips. The bypass

and TDO pins. This enables shifting of data through the SRAM

with minimal delay. The bypass register is set LOW (V

) when

the BYPASS instruction is executed.

Boundary Scan Register

The boundary scan register is connected to all of the input and

output pins on the SRAM. Several No Connect (NC) pins are also

included in the scan register to reserve pins for higher density

devices.

The boundary scan register is loaded with the contents of the

RAM input and output ring when the TAP controller is in the

Capture-DR state and is then placed between the TDI and TDO

pins 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 input and output ring.

The Boundary Scan Order on page 19 shows 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 Definitions on

page 18.

TAP Instruction Set

Eight different instructions are possible with the three-bit

instruction register. All combinations are listed in Instruction

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.

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 pins. To execute

the instruction after it is shifted in, the TAP controller must be

moved into the Update-IR state.

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