19 12-BIT A/D CONVERTER (ADC12A)
19-2
Seiko Epson Corporation
S1C31D50/D51 TECHNICAL MANUAL
(Rev. 2.00)
19.2 Input Pins and External Connections
19.2.1 List of Input Pins
Table 19.2.1.1 lists the ADC12A pins.
Table 19.2.1.1 List of ADC12A Pins
Pin name
I/O
*
Initial status
*
Function
ADINnm
A
Hi-Z
Analog signal input
#ADTRGn
I
I
External trigger input
VREFAn
A
Hi-Z
Reference voltage input
*
Indicates the status when the pin is configured for the ADC12A.
If the port is shared with the ADC12A pin and other functions, the ADC12A input function must be assigned to the
port before activating the ADC12A. For more information, refer to the “I/O Ports” chapter.
19.2.2 External Connections
Figure 19.2.2.1 shows a connection diagram between the ADC12A and external devices.
Sensor output
detection
Battery voltage
detection
S1C31 ADC12A
V
DD
VREFAn
ADINn0
ADINnm
DC-DC
converter
Sensor
3.3 V
Figure 19.2.2.1 Connections between ADC12A and External Devices
19.3 Clock Settings
19.3.1 ADC12A Operating Clock
The 16-bit timer Ch.
k
operating clock CLK_T16_
k
is also used as the ADC12A operating clock. For more informa-
tion on the CLK_T16_
k
settings and clock supply in SLEEP and DEBUG modes, refer to “Clock Settings” in the
“16-bit Timers” chapter.
Note: When the CLK_T16_k supply stops during A/D conversion (e.g., when the CPU enters SLEEP
or DEBUG mode), correct conversion results cannot be obtained even if the clock supply is re-
sumed after that. In this case, perform A/D conversion again.
19.3.2 Sampling Time
The ADC12A includes a sample and hold circuit. The sampling time must be set so that it will satisfy the time re-
quired for acquiring input voltage (t
ACQ
: acquisition time). Figure 19.3.2.1 shows an equivalent circuit of the analog
input portion.
V
DD
V
SS
V
SS
R
ADIN
R
S
:
Source impedance
R
ADIN
: Analog input resistance
C
ADIN
: Analog input capacitance
R
S
ADINnm
C
ADIN
Figure 19.3.2.1 Equivalent Circuit of Analog Input Portion