Toshiba TLCS-900/H1 Series Manual page 311

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 AD conversion, the reference
voltage, 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 a 0 to ADMOD1
<VREFON> in AD mode control register 1. To start AD conversion in the OFF state,
first write a 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 depending on the operation mode of the
AD converter.
• In analog input channel fixed mode (ADMOD0<SCAN> = 0)
Setting ADMOD1<ADCH1:0> selects one of the input pins AN0 to AN3 as the
input channel.
• In analog input channel scan mode (ADMOD0<SCAN> = 1)
Setting ADMOD1<ADCH1:0> selects one of the four scan modes.
Table 3.11.1 illustrates analog input channel selection in each operation mode.
On a reset, ADMOD0<SCAN> is set to 0 and ADMOD1<ADCH1:0> is initialized to
00. 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.
<ADCH1:0>
00
01
10
11
Table 3.11.1 Analog Input Channel Selection
Channel Fixed
<SCAN> = "0"
AN0 AN0
AN0 → AN1
AN1
AN0 → AN1 → AN2
AN2
AN0 → AN1 → AN2 → AN3
AN3
92CH21-309
Channel Scan
<SCAN> = "1"
TMP92CH21
2009-06-19