AMD SC2200 manual Testability Jtag, Mandatory Instruction Support, Optional Instruction Support

Debugging and Monitoring 32580B

Debugging and Monitoring8

8.1Testability (JTAG)

The Test Access Port (TAP) allows board level intercon- nection 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 8-1for 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.

8.1.1Mandatory 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.

8.1.2Optional 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.

8.1.3JTAG Chain

Balls that are not part of the JTAG chain:

•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.

AMD Geode™ SC2200 Processor Data Book 365