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Enhanced Queued Analog-to-Digital Converter (EQADC)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
1155
25.7.1.1
EQADC initialization
The following steps provide an example about how to configure the EQADC controls and how to initialize
the on-chip ADCs and the external device. In this example, all conversion commands will be transferred
through CFIFO0.
1. Load all required configuration commands in the RAM in such way that they form a queue; this
data structure will be referred below as CQueue0.
able to configure the on-chip ADCs and external device at the same time. Although, this example
uses the DMAC to store commands in CFIFO0, configuration commands could have also been
directly written to the CFIFO0 push register.
2. Select source driving EQADC hardware trigger ports (ETRIG). Before proceeding to next step,
allow some time (minimum of two system clocks - filter period is set to minimum after reset) so
that the logic level at the source is filtered and reaches the EQADC control logic.
NOTE
ETRIG ports could be driven by an external pin or by the output port of
other blocks in the device, such as timers. In order to avoid unexpected
triggering of CFIFOs in hardware trigger modes, the source driving the
ETRIG port must be selected and set to a known logic level before putting
the CFIFOs into the WAITING FOR TRIGGER state.
The trigger filter bypass control inputs must be set considering the
characteristics of the trigger signal. A particular case to assert the bypass
control is when a device’s internal signal with one clock width pulse is used.
3. Configure
Section 25.5.2.4, EQADC External Trigger Digital Filter Register (EQADC_ETDFR)
.
4. Configure
Section 25.5.2.3, EQADC null message send format register (EQADC_NMSFR)
.
5. Configure
Section 25.5.2.13, EQADC SSI Control Register (EQADC_SSICR)
, to communicate
with the external device.
6. Enable the EQADC SSI by programming the ESSIE field in the
Section 25.5.2.1, EQADC Module
Configuration Register (EQADC_MCR)
a) Write 0b10 to ESSIE field to enable the EQADC SSI. FCK is free running but serial
transmissions are not started.
b) Wait until the external device becomes stable after reset.
3
Software-triggered
CQueue
every 3.9 ms
3
Command triggered by
software strategy
4
Repetitive
angle-based
CQueue
every 625
s
7
Airflow read every 30
degrees at 8000 RPM
5
Slow repetitive
time-based CQueue
every 100 ms
10
Temperature sensors
Table 25-75. Application of Each CQueue
CQueue
Number
CQueue Type
Running Speed
Number of
Contiguous
Conversions
Example
Содержание MPC5644A
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