PXN20RM Datasheet, PDF (1160/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Nexus Development Interface (NDI)
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.
Table 36-4. NDI Configuration Options
JCOMP Asserted
MCKO_EN bit of PCR
FPM bit of PCR¹
Configuration
No
X
X
Reset
Yes
0
X
Disabled
Yes
1
1 _{FPM must always be set.}
1
Full-Port Mode
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.
Table 36-5. MCKO_DIV Values
MCKO_DIV[2:0]
MCKO Frequency
0b000¹
SYS_CLK
0b001
SYS_CLK/2
0b010
Reserved
0b011
SYS_CLK/4
0b100
Reserved
0b101
Reserved
0b110
Reserved
0b111
SYS_CLK/8
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.
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.
36-10
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor