R01UH0823EJ0100 Rev.1.00 Page 1616 of 1823
Jul 31, 2019
RX23W Group 44. 12-Bit A/D Converter (S12ADE)
44.8.3 A/D Conversion Restarting Timing and Termination Timing
It takes a maximum of six ADCLK cycles for the idle analog unit of the 12-bit A/D converter to be restarted by setting
the ADCSR.ADST bit to 1. It takes a maximum of three ADCLK cycles for the operating analog unit of the 12-bit A/D
converter to be terminated by setting the ADCSR.ADST bit to 0.
44.8.4 Notes on Scan End Interrupt Handling
When scanning the same analog input twice using any trigger, the first A/D-converted data is overwritten with the second
A/D-converted data in the case that the CPU does not complete reading the A/D-converted data by the time the A/D
conversion of the first analog input for the second scan ends after the first scan end interrupt is generated.
44.8.5 Module Stop Function Setting
Operation of the 12-bit A/D converter can be disabled or enabled by setting module stop control register A (MSTPCRA).
The initial setting is for operation of the 12-bit A/D converter to be halted. Register access is enabled by releasing the
module stop state.
After the module stop state is released, wait for 1 μs to start A/D conversion. For details, refer to
section 11, Low
Power Consumption
.
44.8.6 Notes on Entering Low Power Consumption States
Before entering the module stop state or software standby mode, make sure to stop A/D conversion. Here, set the
ADCSR.ADST bit to 0, and secure certain period of time until the analog unit of the 12-bit A/D converter is stopped.
Follow the procedure given below to secure this time.
Follow the procedure for clear operation by software through the ADCSR.ADST bit, shown in
Figure 44.29. After that,
wait for two clock cycles of ADCLK before entering the peripheral module stop state or software standby mode.
44.8.7 Notes on Canceling Software Standby Mode
After software standby mode is canceled, wait until the crystal oscillation stabilization time or the PLL circuit
stabilization time elapses, and then wait for 1 μs before starting A/D conversion. For details, refer to
section 11, Low
Power Consumption
.
44.8.8 Pin Setting when the 12-bit A/D Converter is Used
When the 12-bit A/D converter is used, do not set any pin of port 4 as output.
Output from any of the pins may affect on A/D conversion accuracy because analog power supply is used in the part of
the port 4 circuit.
44.8.9 Error in Absolute Accuracy When Disconnection Detection Assistance is in Use
Using disconnection detection assistance leads to an error in absolute accuracy of the A/D converter. This is because an
error voltage is input to the analog input pins due to the resistive voltage division between the pull-up or pull-down
resistor (Rp) and the resistance of the signal source (Rs). This error in absolute accuracy is calculated from the following
formula. Only use disconnection detection assistance after thorough evaluation.
Maximum error in absolute accuracy (LSB) = 4095 × Rs / Rp
To Next Page
Loading...
Need help?
General
