Nexus Development Interface (NDI)
PXN20 Microcontroller Reference Manual, Rev. 1
36-10 Freescale Semiconductor
When writing to the PCR, the PCR LSB must be written to a logic 0. Setting the LSB of the PCR enables
factory debug mode and prevents the transmission of Nexus messages.
Table 36-4 describes the NDI configuration options.
36.4.1.4 Programmable MCKO Frequency
MCKO is an output clock to the development tools used for the timing of MSEO and MDO pin functions.
MCKO is derived from the system clock, and its frequency is determined by the value of the MCKO_DIV
field in the port configuration register (PCR) located in the NPC. Possible operating frequencies include
SYS_CLK, one-half, one-quarter, and one-eighth SYS_CLK speed.
Table 36-5 shows the MCKO_DIV encodings. In this table, SYS_CLK represents the system clock
frequency.
36.4.1.5 Nexus Messaging
Most of the messages transmitted by the NDI include a SRC field. This field is used to identify which
source generated the message. Table 36-6 shows the values used for the SRC field by the different clients
on the device. These 4-bit values are specific to the device.
Table 36-4. NDI Configuration Options
JCOMP Asserted MCKO_EN bit of PCR FPM bit of PCR
1
1
FPM must always be set.
Configuration
No X X Reset
Ye s 0 X D isa b l e d
Yes 1 1 Full-Port Mode
Table 36-5. MCKO_DIV Values
MCKO_DIV[2:0] MCKO Frequency
0b000
1
1
The SYS_CLK setting for MCKO frequency should only
be used if this setting does not violate the maximum
operating frequency of the auxiliary port pins.
SYS_CLK
0b001 SYS_CLK/2
0b010 Reserved
0b011 SYS_CLK/4
0b100 Reserved
0b101 Reserved
0b110 Reserved
0b111 SYS_CLK/8
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