NXP Semiconductors MPC5644A, Reference Manual, Page: 1684 / 1735

Nexus Port Controller (NPC)
MPC5644A Microcontroller Reference Manual, Rev. 6
1684 Freescale Semiconductor
Figure 37-6 shows the various message formats that the pin interface formatter has to encounter. Note that
for variable-length fields, the transmitted size of the field is determined from the range of the least
significant bit to the most significant non-zero-valued bit (i.e. most significant zero-valued bits are not
transmitted).
The double edges in Figure 37-6 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.
37.5.2.3 Rules of message
• 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 37-7 shows the transmission
sequence of a message that is made up of a TCODE followed by two fields.
Table 37-9. NPC output messages
Message name
Min. packet
size (bits)
Max. packet
size (bits)
Packet type Packet name Packet description
Device ID Message 6 6 fixed TCODE Value = 1
32 32 fixed ID DID register contents
Message TCODE Field #1 Field #2 Field #3 Field #4 Field #5
Min.
size
1
(bits)
Max.
size
2
(bits)
Device ID Message 1 Fixed = 32 NA NA NA NA 38 38
NOTES:
1. Minimum information size. The actual number of bits transmitted depends on the number of MDO pins
2. Maximum information size. The actual number of bits transmitted depends on the number of MDO pins
Figure 37-6. Message Field Sizes