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PARTNUMBER14 Datasheet(PDF) 2 Page - Texas Instruments |
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PARTNUMBER14 Datasheet(HTML) 2 Page - Texas Instruments |
2 / 31 page SN54LVT18502 3.3-V ABT SCAN TEST DEVICE WITH 18-BIT UNIVERSAL BUS TRANSCEIVERS SCBS669 – JULY 1996 2 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 description The SN54LVT18502 scan test device with 18-bit universal bus transceivers is a member of the Texas Instruments SCOPE ™ testability integrated-circuit family. This family of devices supports IEEE Standard 1149.1-1990 boundary scan to facilitate testing of complex circuit-board assemblies. Scan access to the test circuitry is accomplished via the 4-wire test access port (TAP) interface. Additionally, this device is designed specifically for low-voltage (3.3-V) VCC operation, but with the capability to provide a TTL interface to a 5-V system environment. In the normal mode, this device is an 18-bit universal bus transceiver that combines D-type latches and D-type flip-flops to allow data flow in transparent, latched, or clocked modes. It can be used either as two 9-bit transceivers or one 18-bit transceiver. The test circuitry can be activated by the TAP to take snapshot samples of the data appearing at the device pins or to perform a self test on the boundary-test cells. Activating the TAP in the normal mode does not affect the functional operation of the SCOPE ™ universal bus transceivers. Data flow in each direction is controlled by output-enable (OEAB and OEBA), latch-enable (LEAB and LEBA), and clock (CLKAB and CLKBA) inputs. For A-to-B data flow, the device operates in the transparent mode when LEAB is high. When LEAB is low, the A-bus data is latched while CLKAB is held at a static low or high logic level. Otherwise, if LEAB is low, A-bus data is stored on a low-to-high transition of CLKAB. When OEAB is low, the B outputs are active. When OEAB is high, the B outputs are in the high-impedance state. B-to-A data flow is similar to A-to-B data flow, but uses the OEBA, LEBA, and CLKBA inputs. In the test mode, the normal operation of the SCOPE ™ universal bus transceivers is inhibited and the test circuitry is enabled to observe and control the I/O boundary of the device. When enabled, the test circuitry performs boundary-scan test operations according to the protocol described in IEEE Standard 1149.1-1990. Four dedicated test pins are used to observe and control the operation of the test circuitry: test data input (TDI), test data output (TDO), test mode select (TMS), and test clock (TCK). Additionally, the test circuitry performs other testing functions such as parallel-signature analysis (PSA) on data inputs and pseudo-random pattern generation (PRPG) from data outputs. All testing and scan operations are synchronized to the TAP interface. Active bus-hold circuitry is provided to hold unused or floating data inputs at a valid logic level. The SN54LVT18502 is characterized for operation over the full military temperature range of –55 °C to 125°C. FUNCTION TABLE† (normal mode, each register) INPUTS OUTPUT OEAB LEAB CLKAB A B L L L X B0‡ L L ↑ LL L L ↑ HH L HX L L L HX H H H X X X Z † A-to-B data flow is shown. B-to-A data flow is similar but uses OEBA, LEBA, and CLKBA. ‡ Output level before the indicated steady-state input conditions were established |
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