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Boundary Scan Test Interface
Élan™SC520 Microcontroller User’s Manual
25-3
25.4.1
Instruction Register
The Instruction register is a 4-bit register that allows instructions to be serially shifted into
the device. The instruction determines the test to be executed and the data register to be
accessed. The least significant bit is nearest the JTAG_TDO output. When the test access
port (TAP) controller is reset, the Instruction register is loaded with the default instruction
IDCODE.
25.4.1.1
Implemented Instructions
The ÉlanSC520 microcontroller supports all three mandatory boundary-scan instructions:
BYPASS, SAMPLE/PRELOAD, and EXTEST, along with three additional instructions:
IDCODE, HIGHZ and DEBUG.
Table 25-2 shows the test access port (TAP) instructions that are supported on the
ÉlanSC520 microcontroller.
25.4.1.1.1
EXTEST Instruction
The instruction code is 0000b. The EXTEST instruction allows testing of circuitry external
to the component package, typically board interconnects. It does so by driving the values
loaded into the microcontroller’s Boundary Scan register out on to the output pins
corresponding to each boundary scan cell. It then captures the values on the
microcontroller’s input pins to be loaded into their corresponding Boundary Scan register
locations. I/O pins are selected as input or output, depending on the value loaded into their
control setting locations in the Boundary Scan register. Values shifted into input latches in
the Boundary Scan register are never used by the internal logic of the ÉlanSC520
microcontroller.
Note: After using the EXTEST instruction, the ÉlanSC520 microcontroller should be reset
before normal (non-boundary scan) use to ensure the state of the ÉlanSC520
microcontroller.
25.4.1.1.2
SAMPLE/PRELOAD Instruction
The instruction code is 0001b. The SAMPLE/PRELOAD instruction performs two functions.
■
When the TAP controller is in the Capture-DR state, the SAMPLE/PRELOAD instruction
allows a “snapshot” of the normal operation of the ÉlanSC520 microcontroller without
interfering with that normal operation. The instruction causes Boundary Scan register
cells associated with outputs to sample the value being driven by the microcontroller. It
causes the cells associated with inputs to sample the value being driven into the
microcontroller. On both outputs and inputs, the sampling occurs on the rising edge of
JTAG_TCK.
Table 25-2
Test Access Port Instruction Set
Instruction
IR3–IR0
EXTEST
0000
SAMPLE/PRELOAD
0001
IDCODE
0010
HIGHZ
0011
Reserved
0100
DEBUG
0101
Reserved
0110
±
1110
BYPASS
1111
Содержание Elan SC520
Страница 1: ...lan SC520 Microcontroller User s Manual Order 22004A...
Страница 4: ...iv lan SC520 Microcontroller User s Manual...
Страница 28: ...Introduction xxviii lan SC520 Microcontroller User s Manual...
Страница 42: ...Architectural Overview 1 14 lan SC520 Microcontroller User s Manual...
Страница 78: ...System Initialization 3 22 lan SC520 Microcontroller User s Manual...
Страница 108: ...Clock Generation and Control 5 10 lan SC520 Microcontroller User s Manual...
Страница 118: ...Reset Generation 6 10 lan SC520 Microcontroller User s Manual...
Страница 148: ...System Arbitration 8 24 lan SC520 Microcontroller User s Manual...
Страница 214: ...SDRAM Controller 10 36 lan SC520 Microcontroller User s Manual...
Страница 230: ...Write Buffer and Read Buffer 11 16 lan SC520 Microcontroller User s Manual...
Страница 288: ...GP Bus DMA Controller 14 22 lan SC520 Microcontroller User s Manual...
Страница 316: ...Programmable Interval Timer 16 8 lan SC520 Microcontroller User s Manual...
Страница 328: ...Software Timer 18 4 lan SC520 Microcontroller User s Manual...
Страница 346: ...Real Time Clock 20 12 lan SC520 Microcontroller User s Manual...
Страница 360: ...UART Serial Ports 21 14 lan SC520 Microcontroller User s Manual...
Страница 414: ...AMDebug Technology 26 8 lan SC520 Microcontroller User s Manual...