Motorola M68060 User Manual page 262

SECTION 9
IEEE 1149.1 TEST (JTAG) AND
DEBUG PIPE CONTROL MODES
This section describes the IEEE 1149.1 test access port (normal Joint Test Action Group
(JTAG)) mode and the debug pipe control mode, which are available on the MC68060.
9.1 IEEE 1149.1 TEST ACCESS PORT (NORMAL JTAG) MODE
The MC68060 includes dedicated user-accessible test logic that is fully compliant with the
IEEE standard 1149.1-1993 Standard Test Access Port and Boundary Scan Architecture
except in the case where the JTAG architecture and the LPSTOP function interact. This
case is not formally addressed by the standard, but the MC68060 solution is transparent to
the functionality defined by the standard, has the effect of meeting full compatibility to IEEE
1149.1, and has been approved by the IEEE 1149.1 Working Group Committee.
The following description is to be used in conjunction with the supporting IEEE document
listed previously. This section includes the description of those chip-specific items that the
IEEE standard defines as required as well as those items that are specific to the MC68060
implementation.
The MC68060 JTAG test architecture implementation supports circuit board test strategies
that are based on the IEEE standard. This architecture provides access to all of the data and
control pins of the chip from the board-edge connector through the standard four pin test
access port (TAP) plus the additional optional active low TRST reset pin (see Section 2 Sig-
nal Description for a description of TRST). The test logic itself uses a static design and is
entirely independent of the system logic, except where the JTAG mode is subordinate to
another complimentary test mode (see 9.2 Debug Pipe Control Mode ). When placed in the
subordinate mode, the JTAG test logic is placed in reset and the TAP pins are used for alter-
nate purposes in accordance with the rules and restrictions set forth for the use of a JTAG
compliance enable pin.
The MC68060 JTAG implementation provides the capabilities to:
1. Perform boundary scan operations to test circuit board electrical continuity,
2. Bypass the MC68060 by reducing the shift register path to a single cell,
3. Sample the MC68060 system pins during operation and transparently shift out the
result,
4. Set the MC68060 output drive pins to fixed logic values while reducing the shift register
path to a single cell, and
5. Protect the MC68060 system output and input pins from backdriving and random
MOTOROLA M68060 USER'S MANUAL 9-1