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AMD Geode™ SC1200/SC1201 Processor Data Book 363
8
Debugging and Monitoring 32579B
8.0Debugging and Monitoring
8.1 Testability (JTAG)
The Test Access Port (TAP) allows board level interconnec-
tion verification and chip production tests. An IEEE-
1149.1a compliant test interface, TAP supports all IEEE
mandatory instructions as well as several optional instruc-
tions for added functionality. See Table 8-1 for a summary
of all instructions support. For further information on JTAG,
refer to IEEE Standard 1149.1a-1993 Test Access Port and
Boundary-Scan Architecture.
8.1.1 Mandatory Instruction Support
The TAP supports all IEEE mandatory instructions, includ-
ing:
• BYPASS.
Presents the shortest path through a given chip (a 1-bit
shift register).
• EXTEST
Drives data loaded into the JTAG path (possibly with a
SAMPLE/PRELOAD instruction) to output pins.
• SAMPLE/PRELOAD
Captures chip inputs and outputs.
8.1.2 Optional Instruction Support
The TAP supports the following IEEE optional instructions:
• IDCODE
Presents the contents of the Device Identification
register in serial format.
• CLAMP
Ensures that the Bypass register is connected between
TDI and TDO, and then drives data that was loaded into
the Boundary Scan register (e.g., via SAMPLE-
PRELOAD instruction) to output signals. These signals
do not change while the CLAMP instruction is selected.
• HIZ
Puts all chip outputs in inactive (floating) state
(including all pins that do not require a TRI-STATE
output for normal functionality). Note that not all pull-up
resistors are disabled in this state.
8.1.3 JTAG Chain
Balls that are not part of the JTAG chain:
• TV DACs
• CRT DACs
• USB I/Os
Table 8-1. JTAG Mode Instruction Support
Code Instruction Activity
000 EXTEST Drives shifted data to output pins.
001 SAMPLE/PRELOAD Captures inputs and system outputs.
010 IDCODE Scans out device identifier.
011 HIZ Puts all output and bidirectional pins in TRI-STATE mode.
100 CLAMP Drives fixed data from Boundary Scan register.
101 Reserved
110 Reserved
111 BYPASS Presents shortest external path through device.