NXP Semiconductors PXN2020, Reference Manual, Page: 1169 / 1376

Nexus Development Interface (NDI)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 36-19
36.5.5.2.2 Output Messages
In addition to sending out messages generated in other Nexus modules, the NPC can also output the device
ID message contained in the device ID register on the MDO pins. The device ID message can also be sent
out serially through TDO.
Table 36-10 describes the device ID message that the NPC can transmit on the auxiliary port. The TCODE
is the first packet transmitted.
Figure 36-9 shows the various message formats that the pin interface formatter has to encounter.
The double edges in Figure 36-9 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.
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 36-10 shows the transmission
sequence of a message that is made up of a TCODE followed by three fields.
Table 36-10. 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
Figure 36-9. Message Field Sizes
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 NA NA NA NA 38 38