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Rev.1.10 Jul 01, 2005 page 195 of 318
REJ09B0124-0110
M16C/6N Group (M16C/6NK, M16C/6NM) 15. A/D Converter
Under development
This document is under development and its contents are subject to change.
15.2 Function
15.2.1 Resolution Select Function
The desired resolution can be selected using the BITS bit in the ADCON1 register. If the BITS bit is set to
“1” (10-bit conversion accuracy), the A/D conversion result is stored in the bit 0 to bit 9 in the ADi register
(i = 0 to 7). If the BITS bit is set to “0” (8-bit conversion accuracy), the A/D conversion result is stored in the
bit 0 to bit 7 in the ADi register.
15.2.2 Sample and Hold
If the SMP bit in the ADCON2 register is set to “1” (with sample-and-hold), the conversion speed per pin
is increased to 28 φAD cycles for 8-bit resolution or 33 φAD cycles for 10-bit resolution. Sample-and-hold
is effective in all operation modes. Select whether or not to use the sample and hold function before
starting A/D conversion.
15.2.3 Extended Analog Input Pins
In one-shot and repeat modes, the ANEX0 and ANEX1 pins can be used as analog input pins. Use the
OPA1 to OPA0 bits in the ADCON1 register to select whether or not use ANEX0 and ANEX1.
The A/D conversion results of ANEX0 and ANEX1 inputs are stored in the AD0 and AD1 registers,
respectively.
15.2.4 External Operation Amplifier (Op-Amp) Connection Mode
Multiple analog inputs can be amplified using a single external op-amp via the ANXE0 and ANEX1 pins.
Set the OPA1 to OPA0 bits in the ADCON1 register to “11b” (external op-amp connection mode). The
inputs from ANi (i = 0 to 7)
(1)
are output from the ANEX0 pin. Amplify this output with an external op-amp
before sending it back to the ANEX1 pin. The A/D conversion result is stored in the corresponding ADi
register. The A/D conversion speed depends on the response characteristics of the external op-amp.
Figure 15.9 shows an example of how to connect the pins in external operation amp.
NOTE:
1. AN0_i and AN2_i can be used the same as ANi.
ADGSEL1 to ADGSEL0 bits in ADCON2 register = 00b
Successive conversion
register
Comparator
External op-amp
ANEX0
ANEX1
ADGSEL1 to ADGSEL0 bits = 10b
ADGSEL1 to ADGSEL0 bits = 11b
Resistor ladder
Microcomputer
AN0
AN1
AN2
AN3
AN4
AN5
AN6
AN7
AN0_0
AN0_1
AN0_2
AN0_3
AN0_4
AN0_5
AN0_6
AN0_7
AN2_0
AN2_1
AN2_2
AN2_3
AN2_4
AN2_5
AN2_6
AN2_7
Figure 15.9 External Op-Amp Connection