Toshiba TMP91C815F Data Book page 189

3.11.2 Description of operation
(1) Analog reference voltage
A High-level analog reference voltage is applied to the VREFH pin; a low-level analog reference
voltage is applied to the VREFL pin. To perform A/D conversion, the reference voltage as the
difference between VREFH and VREFL, is divided by 1024 using string resistance. The result of
the division is then compared with the analog input voltage.
To turn off the switch between VREFH and VREFL, write "0" to ADMOD1<VREFON> in A/D
Mode Control Register 1. To start A/D conversion in the OFF state, first write "1" to
ADMOD1<VREFON>, wait 3 μs until the internal reference voltage stabilizes (this is not related
to fc), then set ADMOD0< ADS> to "1".
(2) Analog input channel selection
The analog input channel selection varies depends on the operation mode of the A/D converter.
• In Analog Input Channel Fixed Mode (A/D MOD0<SCAN> = "0")
Setting ADMOD1<ADCH2 to ADCH0> selects one of the input pins AN0 to AN7 as the input
channel.
• In Analog Input Channel Scan Mode (ADMOD0<SCAN> = "1")
Setting ADMOD1<ADCH2 to ADCH0> selects one of the 8 scan modes.
Table 3.11.1 illustrates analog input channel selection in each operation mode.
After Reset, ADMOD0<SCAN> = "0" and ADMOD1<ADCH2 to ADCH0> = "000". Thus pin
AN0 is selected as the fixed input channel. Pins not used as analog input channels can be used as
standard input port pins.
<ADCH2~0>
000
001
010
011
100
101
110
111
Table 3.11.1 Analog input channel selection
Channel fixed
<SCAN> = "0"
AN0
AN1
AN2
AN3
AN4
AN5
AN6
AN7
91C815-186
Channel scan
<SCAN> = "1"
AN0
AN0 → AN1
AN0 → AN1 → AN2
AN0 → AN1 → AN2 → AN3
AN4
AN4 → AN5
AN4 → AN5 → AN6
AN4 → AN5 → AN6 → AN7
TMP91C815