218
μPD780948, μPD78F0948, μPD780949, μPD78F0949
13.4.3 A/D converter operation mode
The operation mode of the A/D converter is the select mode. One analog input channel is selected from
among ANI0 to ANI7 with the analog input channel specification register (ADS1) and A/D conversion is
performed.
The following two types of functions can be selected by setting the PFEN flag of the PFM register.
(1) Normal 8-bit A/D converter (PFEN = 0)
(2) Power-fail detection function (PFEN = 1)
(1) A/D conversion (when PFEN = 0)
When bit 7 (ADCS1) of the A/D converter mode register (ADM1) is set to 1 and bit 7 of the power-
fail compare mode register (PFM) is set to 0, A/D conversion of the voltage applied to the analog
input pin specified with the analog input channel specification register (ADS1) starts.
Upon the end of the A/D conversion, the conversion result is stored in the A/D conversion result
register (ADCR1), and the interrupt request signal (INTAD) is generated. After one A/D conversion
operation is started and ended, the next conversion operation is immediately started. A/D conversion
operations are repeated until new data is written to ADS1.
If ADS1 is rewritten during A/D conversion operation, the A/D conversion operation under execution
is stopped, and A/D conversion of a newly selected analog input channel is started.
If data with ADCS1 set to 0 is written to ADM1 during A/D conversion operation, the A/D conversion
operation stops immediately.
(2) Power-fail detection function (when PFEN = 1)
When bit 7 (ADCS1) of the A/D converter mode register (ADM1) and bit 7 (PFEN) of the power-fail
compare mode register (PFM) are set to 1, A/D conversion of the voltage applied to the analog input
pin specified with the analog input channel specification register (ADS1) starts.
Upon the end of the A/D conversion, the conversion result is stored in the A/D conversion result
register (ADCR1), compared with the value of the power-fail compare threshold value register (PFT),
and INTAD is generated under the condition specified by the PFCM flag of the PFM register.
Caution:
When executing power-fail comparison, the interrupt request signal (INTAD) is not
generated on completion of the first conversion after ADCS1 has been set to 1. INTAD
is valid from completion of the second conversion.