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IS61LF25636A Datasheet(PDF) 20 Page - Integrated Silicon Solution, Inc |
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IS61LF25636A Datasheet(HTML) 20 Page - Integrated Silicon Solution, Inc |
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20 / 32 page  20 Integrated Silicon Solution, Inc. — 1-800-379-4774 Rev. A 05/04/05 ISSI® IS61LF25636A IS61LF51218A IS61VF25636A IS61VF51218A TEST DATA OUT (TDO) The TDO output pin is used to serially clock data-out from the registers. The output is active depending on the current state of the TAP state machine (see TAP Controller State Diagram). The output changes on the falling edge of TCK and TDO is connected to the Least Significant Bit (LSB) of any register. PERFORMING A TAP RESET A Reset is performed by forcing TMS HIGH (VDD) for five rising edges of TCK. RESET may be performed while the SRAM is operating and does not affect its operation. At power-up, the TAP is internally reset to ensure that TDO comes up in a high-Z state. TAP REGISTERS Registers are connected between the TDI and TDO pins 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 registers. Data is serially loaded into the TDI pin on the rising edge of TCK and output on the TDO pin on the falling edge of TCK. Instruction Register Three-bit instructions can be serially loaded into the in- struction register. This register is loaded when it is placed between the TDI and TDO pins. (See TAP Controller Block Diagram) At 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 previously described. When the TAP controller is in the CaptureIR 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 states. The bypass register is a single-bit register that can be placed between TDI and TDO pins. This allows data to be shifted through the SRAM with minimal delay. The bypass register is set LOW (Vss) when the BYPASS instruction is ex- ecuted. Boundary Scan Register The boundary scan register is connected to all 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 x36 configuration has a 75-bit-long register and the x18 configuration also has a 75-bit-long register. 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 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 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 to 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 vendor code and other information described in the Identification Register Definitions table. Scan Register Sizes Register Name Bit Size Bit Size (x18) (x36) Instruction 3 3 Bypass 1 1 ID 32 32 Boundary Scan 75 75 IDENTIFICATION REGISTER DEFINITIONS Instruction Field Description 256K x 36 512K x 18 Revision Number (31:28) Reserved for version number. xxxx xxxx Device Depth (27:23) Defines depth of SRAM. 256K or 512K 00111 01000 Device Width (22:18) Defines with of the SRAM. x36 or x18 00100 00011 ISSI Device ID (17:12) Reserved for future use. xxxxx xxxxx ISSI JEDEC ID (11:1) Allows unique identification of SRAM vendor. 00011010101 00011010101 ID Register Presence (0) Indicate the presence of an ID register. 1 1 |
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