A-D CONVERTER
12.2 Block description
(1) Analog input pin select bits (bits 0 to 2 at address 1E16
)
These bits are used to select an analog input pin in the one-shot mode or repeat mode. Pins which
are not selected as analog input pins serve as programmable I/O port pins.
Also, these bits must be specified again if the user switches the operation mode to the one-shot
mode or repeat mode after the operation is performed in the single sweep mode or repeat sweep
mode 0.
(2) A-D operation mode select bits (bits 3 and 4 at address 1E16
)
These bits are used to select the operation mode of the A-D converter.
(3) A-D conversion start bit (bit 6 at address 1E16
)
Setting this bit to “1” generates a trigger, causing the A-D converter to start its operation. Clearing
this bit to “0” causes the A-D converter to halt its operation.
In the one-shot mode or single sweep mode, this bit is cleared to “0” when the operation is completed.
In the repeat mode or repeat sweep mode 0, the A-D converter continues its operation until this bit
is cleared to “0” by software.
(4) A-D conversion frequency (φAD) select bit 0 (bit 7 at address 1E16), A-D conversion frequency
(φAD) select bit 1 (bit 4 at address 1F16
)
These bits are used to select the operation clock (φAD) of the A-D converter. Table 12.2.1 lists the
conversion time per one analog input pin.
Since the A-D converter’s comparator consists of capacity coupling amplifiers, be sure to keep that
φAD ≥ 250 kHz while the A-D converter is active.
Table 12.2.1 Conversion time per one analog input pin
Conversion time (µs) (Note)
A-D conversion
frequency (φAD)
select bit 1
A-D conversion
frequency (φAD)
select bit 0
fsys = 20 MHz
φAD
10-bit resolution
mode
Comparator
function
5.60
8-bit resolution
mode
0
0
1
1
0
1
0
1
f2 divided by 4
19.60
23.60
f2 divided by 2
9.80
11.80
2.80
f2
4.90
5.90
1.40
f1
2.45
Do not select.
0.70
Note: This applies when the peripheral devices’ clock select bits 0, 1 (bits 6, 7 at address BC16) = “00
2
.”
(5) A-D sweep pin select bits (bits 0 and 1 at address 1F16
)
These bits are used to select analog input pins in the single sweep mode or repeat sweep mode 0.
Pins which are not selected as analog input pins serve as programmable I/O port pins or as I/O pins
of other internal peripheral devices, which are multiplexed.
(6) Resolution select bit (bit 3 at address 1F16
)
This bit is used to select a resolution.
(7)
VREF connection select bit (bit 6 at address 1F16)
When the A-D converter is not used, this bit is used to disconnect the resistor ladder network of the
A-D converter from the reference voltage input pin (VREF).
When the resistor ladder network is disconnected from pin VREF, the current is not flowed from pin
V
REF to resistor ladder network. Accordingly, the power dissipation can be saved.
When this bit changes from “1” (VREF disconnected) to “0” (VREF connected), start of the operation
must be 1 µs or more later.
7906 Group User’s Manual Rev.2.0
12-7
RENESAS [ RENESAS TECHNOLOGY CORP ]
