PXN20RM Datasheet, PDF (1125/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Analog-to-Digital Converter (ADC)
The clock stretching is implemented if and only if MCR[ADCLKSEL] = 0 (if AD_clk is half ipg_clk).
In order to support different loadings and switching times (in particular for the group 2 channels), three
different Conversion Timing registers are present (CTR[0 – 2]). The first is associated with group 0
channels, the second one with group 1 channels, and the third one with the group 2 channels. INPLATCH
and IPCMP configurations are limited when ipg_clk frequency is greater than 20 Mhz.
34.4.3 ADC Cross Triggering Unit
The ADC Cross Triggering Unit (CTU) is included to enhance the injected conversion capability of the
ADC. The CTU contains multiple event inputs that can be used to select the channels to be converted from
the appropriate event configuration register. In Figure 34-42 the CTU/ADC interface is shown. The CTU
generates a trigger output pulse (ctu_trigger) of one clock cycle and outputs onto a data bus
(ctu_numchannel) which channel has to be converted. A single channel is converted for each request. After
performing the conversion, the ADC returns the result on the ctu_dataout bus. Together with the converted
data, the ADC outputs two pulses named ctu_nextcmd and ctu_push spaced one clock cycle (of analog
AD_clk) apart. The ctu_nextcmd is set to ‘1’ during the last clock cycle of ADC evaluation phase. The
ctu_push is asserted when the conversion is finished, meaning that the ctu_dataout is valid. After
performing the conversion, the conversion result is saved in the corresponding data register and it is
compared with Watchdog thresholds if requested.
ctu_trigger
ctu_numchannel<num_ch_bits-1:0>
CTU
ctu_nextcmd
ctu_push
ctu_dataout<9:0>
ADC
Digital
Interface
Figure 34-42. ADC Cross Triggering Unit
Two different modes can be selected by programming the CTUEN field of MCR, as described in
Table 34-41:
Table 34-41. CTU Selection
CTUEN
CTU Mode
0
CTU is disabled.
1
CTU Trigger Mode is enabled.
When the CTU is enabled, the CPU is able to write in the ADC registers but the CPU cannot start any
conversion. Conversion requests can be generated only by the CTU trigger pulse. If a normal or injected
conversion is requested, it is automatically discarded. When the CTU sends to the ADC the number of the
Freescale Semiconductor
PXN20 Microcontroller Reference Manual, Rev. 1
34-45