Cypress CY7C1474V25 manual IEEE 1149.1 Serial Boundary Scan JTAG, TAP Controller Block Diagram

CY7C1470V25

CY7C1472V25

CY7C1474V25

IEEE 1149.1 Serial Boundary Scan (JTAG)

The CY7C1470V25/CY7C1472V25/CY7C1474V25 incorpo- rates a serial boundary scan test access port (TAP). This port operates in accordance with IEEE Standard 1149.1-1990 but does not have the set of functions required for full 1149.1 compliance. These functions from the IEEE specification are excluded because their inclusion places an added delay in the critical speed path of the SRAM. Note that the TAP controller functions in a manner that does not conflict with the operation of other devices using 1149.1 fully compliant TAPs. The TAP operates using JEDEC-standard 2.5V or 1.8V I/O logic levels.

The CY7C1470V25/CY7C1472V25/CY7C1474V25 contains a TAP controller, instruction register, boundary scan register, bypass register, and ID register.

Disabling the JTAG Feature

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. It is allowable to leave this ball unconnected if the TAP is not used. The ball is pulled up internally, resulting in a logic HIGH level.

Test Data-In (TDI)

The TDI ball is used to serially input information into the registers and can be connected to the input of any of the registers. The register between TDI and TDO is chosen by the instruction that is loaded into the TAP instruction register. For information on loading the instruction register, see the TAP Controller State Diagram. 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) of any register. (See Tap Controller Block Diagram.)

It is possible to operate the SRAM without using the JTAG feature. To disable the TAP controller, TCK must be tied LOW (VSS) to prevent clocking of the device. TDI and TMS are inter- nally pulled up and may be unconnected. They may alternately be connected to VDD through a pull-up resistor. TDO should be left unconnected. Upon power-up, the device will come up in a reset state which will not interfere with the operation of the device.

Test Data-Out (TDO)

The TDO output ball is used to serially clock data-out from the registers. The output is active depending upon the current state of the TAP state machine. The output changes on the falling edge of TCK. TDO is connected to the least significant bit (LSB) of any register. (See Tap Controller State Diagram.)

TAP Controller Block Diagram

TAP Controller State Diagram

1	TEST-LOGIC
	RESET
	0
0	RUN-TEST/	1	SELECT	1	SELECT	1
	IDLE		DR-SCAN		IR-SCAN
			0		0
			1		1
			CAPTURE-DR		CAPTURE-IR
			0		0
			SHIFT-DR	0	SHIFT-IR	0
			1		1
			EXIT1-DR	1	EXIT1-IR	1

TDI

Selection Circuitry

									0
			Bypass Register
							2	1	0
	Instruction Register
	31	30	29	.	.	.	2	1	0
Identification Register
	x	.	.	.	.	.	2	1	0

Boundary Scan Register

Selection Circuitry

TDO

	0			0
PAUSE-DR		0	PAUSE-IR		0
	1			1
0			0
EXIT2-DR			EXIT2-IR
	1			1
UPDATE-DR			UPDATE-IR
1	0		1	0

TCK

TMS TAP CONTROLLER

Performing a TAP Reset

A RESET is performed by forcing TMS HIGH (VDD) for five rising edges of TCK. This RESET does not affect the operation of the SRAM and may be performed while the SRAM is operating.

The 0/1 next to each state represents the value of TMS at the rising edge of TCK.

Test Access Port (TAP)

Test Clock (TCK)

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.

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 balls and allow 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.

Document #: 38-05290 Rev. *I Page 10 of 28

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