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參數(shù)資料
| 型號： | SN74ABT18504PMRG4 |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | 總線收發(fā)器 |
| 英文描述： | ABT SERIES, 20-BIT BOUNDARY SCAN REG TRANSCEIVER, TRUE OUTPUT, PQFP64 |
| 封裝： | GREEN, PLASTIC, LQFP-64 |
| 文件頁數(shù)： | 30/32頁 |
| 文件大?。?/td> | 505K |
| 代理商： | SN74ABT18504PMRG4 |
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SN54ABT18504, SN74ABT18504
SCAN TEST DEVICES WITH
20-BIT UNIVERSAL BUS TRANSCEIVERS
SCBS108B – AUGUST 1992 – REVISED JUNE 1993
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
7
state diagram description
The test access port (TAP) controller is a synchronous finite state machine that provides test control signals
throughout the device. The state diagram is illustrated in Figure 1 and is in accordance with IEEE Standard
1149.1-1990. The TAP controller proceeds through its states based on the level of TMS at the rising edge of
TCK.
As illustrated, the TAP controller consists of sixteen 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 though 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 may 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
′ABT18504, the instruction register is reset to the binary value 10000001, which selects the IDCODE
instruction. Each bit in the boundary-scan register is reset to logic 0 except bits 87 – 86, which are reset to logic 1.
The boundary-control register is reset to the binary value 00000000000000000000010, which selects the PSA
test operation with no input masking.
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 can also be entered following data register or instruction register scans.
Run-Test/Idle is provided as a stable state in which the test logic may 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 are provided to 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.
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