
MB91460P Series
DS07-16615-2E
41
■ A/D CONVERTER / RANGE COMPARATOR (MB91F467PA)
The new A/D Converter with Range Comparator is available on MB91FV460B and MB91F467PA and is backward
compatible to the A/D converter used on older devices.
This chapter provides an overview of the A/D converter, describes the register structure and functions, and
describes the operation of the A/D converter.
1.
Overview of A/D Converter and A/D Range Comparator
The A/D converter converts analog input voltages into digital values and provides the following features. Any
ADC channel can be assigned to one of 4 Range Comparators.
1.1.
Features of the A/D converter:
Conversion time: minimum 1
μs per channel.
RC type successive approximation conversion with sample & hold circuit
10-bit or 8-bit resolution
Program section analog input from 32 channels
1 common result data register and 32 dedicated channel result data registers
Single conversion mode:
Convert the specified channel(s) only once.
Continuous mode:
Repeatedly convert the specified channels.
Scan conversion mode:
Continuous conversion of multiple channels, programmable for up to 32 channels
Stop mode:
Convert one channel, then temporarily halt until the next activation.
(Enables synchronization of the conversion start timing.)
A/D conversion can be followed by an A/D conversion interrupt request to CPU. This interrupt, an option that
is ideal for continuous processing can be used to start a DMA transfer of the results of A/D conversion to
memory.
A/D conversion of all enabled channels (scan conversion) can be followed by an A/D End of Scan interrupt
request to CPU. The data is stored into dedicated channel result registers, which can be read out using DMA
transfer.
Conversion startup may be by software, external trigger (falling edge) or timer (rising edge).
1.2.
Features of the A/D Range Comparator (RCO):
4 conversion result Range Comparator channels, comparing the upper 8 bit of the conversion result with an
upper and a lower threshold. The thresholds are programmable for the 4 comparators independently.
Any ADC channel can be assigned to one of the 4 range comparators.
The comparison results will set “overflow” and “interrupt” flags per ADC channel, depending on the configu-
ration. It is possible to configure the comparison for:
- “out of range”: The flags are set if the A/D result is below the lower OR above the upper threshold.
- “inside range”: The flags are set if the A/D result is above the lower AND below the upper threshold.
The configuration can be set individually per ADC channel.
Range comparison can be followed by an A/D Range Comparator interrupt request to CPU.
2.
A/D Converter Input Impedance
The following figure shows the sampling circuit of the A/D converter:
Analog
signal
source
Rext
Rin
Cin
ADC
ANx
Analog SW
Do not set Rext over maximum sampling time (Tsamp).
Rext = Tsamp / (7*Cin) - Rin