AMD SC1201 Computer Hardware User Manual


 
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.