参数资料
型号: SN74LVTH182516
厂商: Texas Instruments, Inc.
英文描述: 3.3-V ABT Scan Test Device With 18-Bit Universal Bus Transceivers(3.3V ABT扫描测试装置(18位通用总线收发器))
中文描述: 的3.3V ABT生根粉扫描测试设备与18位通用总线收发器(3.3V的ABT生根粉扫描测试装置(18位通用总线收发器))
文件页数: 8/36页
文件大小: 769K
代理商: SN74LVTH182516
SN54LVTH18516, SN54LVTH182516, SN74LVTH18516, SN74LVTH182516
3.3-V ABT SCAN TEST DEVICES
WITH 18-BIT UNIVERSAL BUS TRANSCEIVERS
SCBS672B – AUGUST 1996 – REVISED JUNE 1997
8
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
state diagram description
The TAP controller is a synchronous finite state machine that provides test control signals throughout the device.
The state diagram shown in Figure 2 is in accordance with IEEE Std 1149.1-1990. The TAP controller proceeds
through its states based on the level of TMS at the rising edge of TCK.
As shown, the TAP controller consists of 16 states. There are six stable states (indicated by a looping arrow in
the state diagram) and ten unstable states. A stable state is defined as a state the TAP controller can retain for
consecutive TCK cycles. Any state that does not meet this criterion is an unstable state.
There are two main paths through the state diagram: one to access and control the selected data register and
one to access and control the instruction register. Only one register can be accessed at a time.
Test-Logic-Reset
The device powers up in the Test-Logic-Reset state. In the stable Test-Logic-Reset state, the test logic is reset
and is disabled so that the normal logic function of the device is performed. The instruction register is reset to
an opcode that selects the optional IDCODE instruction, if supported, or the BYPASS instruction. Certain data
registers can also be reset to their power-up values.
The state machine is constructed such that the TAP controller returns to the Test-Logic-Reset state in no more
than five TCK cycles if TMS is left high. The TMS pin has an internal pullup resistor that forces it high if left
unconnected or if a board defect causes it to be open circuited.
For the ’LVTH18516 and ’LVTH182516, the instruction register is reset to the binary value 10000001, which
selects the IDCODE instruction. Bits 45–44 are reset to logic 1, ensuring that these cells, which control A-port
and B-port outputs, are set to benign values (i.e., such that if test mode were invoked the outputs would be at
high-impedance state). Reset values of other bits in the boundary-scan register should be considered
indeterminate. The boundary-control register is reset to the binary value 010, which selects the PSA test
operation.
Run-Test/Idle
The TAP controller must pass through the Run-Test/Idle state (from Test-Logic-Reset) before executing any test
operations. The Run-Test/Idle state also can be entered following data-register or instruction-register scans.
Run-Test/Idle is a stable state in which the test logic can be actively running a test or can be idle. The test
operations selected by the boundary-control register are performed while the TAP controller is in the
Run-Test/Idle state.
Select-DR-Scan, Select-lR-Scan
No specific function is performed in the Select-DR-Scan and Select-lR-Scan states, and the TAP controller exits
either of these states on the next TCK cycle. These states allow the selection of either data-register scan or
instruction-register scan.
Capture-DR
When a data-register scan is selected, the TAP controller must pass through the Capture-DR state. In the
Capture-DR state, the selected data register can capture a data value as specified by the current instruction.
Such capture operations occur on the rising edge of TCK, upon which the TAP controller exits the Capture-DR
state.
Shift-DR
Upon entry to the Shift-DR state, the data register is placed in the scan path between TDI and TDO, and on the
first falling edge of TCK, TDO goes from the high-impedance state to an active state. TDO enables to the logic
level present in the least-significant bit of the selected data register.
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