Nexus
MPC5566 Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor 25-19
Figure 25-6 shows the various message formats that the pin interface formatter has to encounter.
Figure 25-6. Message Field Sizes
The double edges in Figure 25-6 indicate the starts and ends of messages. Fields without shaded areas
between them are grouped into super-fields and can be transmitted together without end-of-packet
indications between them.
25.7.2.2.1 Rules of Messages
The rules of messages include the following:
• A variable-sized field within a message must end on a port boundary. (Port boundaries depend on
the number of MDO pins active with the current reset configuration.)
• A variable-sized field may start within a port boundary only when following a fixed-length field.
• Super-fields must end on a port boundary.
• When a variable-length field is sized such that it does not end on a port boundary, it is necessary
to extend and zero fill the remaining bits after the highest order bit so that it can end on a port
boundary.
• Multiple fixed-length packets may start and/or end on a single clock.
• When any packet follows a variable-length packet, it must start on a port boundary.
• The field containing the TCODE number is always transferred out first, followed by subsequent
fields of information.
• Within a field, the lowest significant bits are shifted out first. Figure 25-7 shows the transmission
sequence of a message that is made up of a TCODE followed by three fields.
Figure 25-7. Transmission Sequence of Messages
25.7.2.3 IEEE® 1149.1-2001 (JTAG) TAP
The NPC uses the IEEE® 1149.1-2001 TAP for accessing registers. Each of the individual Nexus modules
on the device implements a TAP controller for accessing its registers as well. TAP signals include TCK,
TDI, TMS, and TDO. Detailed information about the TAP controller state machine may be found in
Section 24.4.3, “TAP Controller State Machine.”
Message TCODE Field #1 Field #2 Field #3 Field #4 Field #5
Min.
Size
1
Bits
1
Minimum information size. The actual number of bits transmitted depends on the number of MDO pins
Max.
Size
2
Bits
2
Maximum information size. The actual number of bits transmitted depends on the number of MDO pins
Device ID Message 1 Fixed = 32
N/A N/A N/A N/A 38 38
FIELD #3
MSB LSB
123
FIELD #2 FIELD #1 TCODE
4
6 bits
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