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MOTOROLA M68040 USER’S MANUAL C- 11
TDI—A test data input with an internal pullup resistor sampled on the rising edge of
TCK.
TDO—A three-state test data output actively driven only in the shift-IR and shift-DR
controller states that changes on the falling edge of TCK.
The test logic also includes an instruction shift register and two test data registers, a
boundary scan register and a bypass register. The boundary scan register links all device
signal pins into a chain that can be controlled by the 3-bit instruction shift register.
TDI
TDO
TMS
TCK
3-BIT INSTRUCTION SHIFT REGISTER
LATCHED DECODER
188-BIT BOUNDARY SCAN REGISTER
TEST DATA REGISTERS
BYPASS
MUX
TAP
CONTROLLER
MUX
187 0
02
Figure C-4. MC68040V and MC68EC040V Test Logic Block Diagram
C.6.1 Instruction Shift Register
The MC68040V and MC68EC040V IEEE standard 1149.1A implementations include a 3-
bit instruction shift register without parity. The register shifts one of six instructions, which
can either select the test to be performed or access a test data register, or both. Data is
transferred from the instruction shift register to latched decoded outputs during the
update-IR state. The instruction shift register is reset to all ones in the TAP controller test-
logic-reset state, which is equivalent to selecting the BYPASS instruction. During the
capture-IR state, the binary value 001 is loaded into the parallel inputs of the instruction
shift register.
The MC68040V and MC68EC040V IEEE standard 1149.1A implementations include three
mandatory standard public instructions (BYPASS, SAMPLE/PRELOAD, and EXTEST),
two optional public standard instructions, and one manufacturer's private instruction. The
five public instructions provide the capability to disable all device output drivers, operate
the device in a BYPASS configuration, and conduct boundary scan test operations. Table
C-3 lists the three bits used in the instruction shift register to decode the instructions and
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