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SN74BCT8245ADWRE4 Datasheet(PDF) 9 Page - Texas Instruments |
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SN74BCT8245ADWRE4 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 29 page SN54BCT8245A, SN74BCT8245A SCAN TEST DEVICES WITH OCTAL BUS TRANSCEIVERS SCBS043E – MAY 1990 – REVISED JULY 1996 9 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 data register description boundary-scan register The boundary-scan register (BSR) is 18 bits long. It contains one boundary-scan cell (BSC) for each normal-function input pin and one BSC for each normal-function output pin. Which I/O ports, A or B, function as input terminals and which function as output terminals is determined by the DIR signal (BSC17) as described below. The BSR is used 1) to store test data that is to be applied internally to the inputs of the normal on-chip logic and/or externally to the device output terminals, and/or 2) to capture data that appears internally at the outputs of the normal on-chip logic and/or externally at the device input terminals. The source of data to be captured into the BSR during Capture-DR is determined by the current instruction. The contents of the BSR may change during Run-Test/Idle, as determined by the current instruction. The contents of the BSR are not changed in Test-Logic-Reset. The BSR order of scan is from TDI through bits 17–0 to TDO. Table 1 shows the BSR bits and their associated device pin signals. The device signals I1–I8 and O1–O8 represent data input signals and data output signals, respectively. The direction control signal (DIR) as output by BSC17 determines which port, A or B, is considered an input and which is considered an output. When the output of BSC17 is logic 0, the device signals I1–I8 are associated with I/O ports B1–B8, while device signals O1–O8 are associated with I/O ports A1–A8. When the output of BSC17 is logic 1, the converse is true (that is, I1–I8 are associated with A1–A8, while O1–O8 are associated with B1–B8). In normal-function mode, the output of the BSC17 input is equivalent to the input signal present at the DIR input pin. Table 1. Boundary-Scan Register Configuration BSR BIT NUMBER DEVICE SIGNAL BSR BIT NUMBER DEVICE SIGNAL BSR BIT NUMBER DEVICE SIGNAL 17 DIR 15 I1 7 O1 16 OE 14 I2 6 O2 – – 13 I3 5 O3 – – 12 I4 4 O4 – – 11 I5 3 O5 – – 10 I6 2 O6 – – 9 I7 1 O7 – – 8 I8 0 O8 boundary-control register The boundary-control register (BCR) is two bits long. The BCR is used in the context of the RUNT instruction to implement additional test operations not included in the basic SCOPE ™ instruction set. Such operations include PRPG and PSA. Table 3 shows the test operations that are decoded by the BCR. During Capture-DR, the contents of the BCR are not changed. At power up or in Test-Logic-Reset, the BCR is reset to the binary value 10, which selects the PSA test operation. The BCR order of scan is shown in Figure 3. TDO TDI Bit 0 (LSB) Bit 1 (MSB) Figure 3. Boundary-Control Register Order of Scan |
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