A-D CONVERTER
7902 Group User’s Manual
13-6
13.2 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 A-D conversion is performed in the single sweep mode or repeat
sweep mode.
(2)
A-D operation mode select bit (bits 3 and 4 at address 1E16)
These bits are used to select the operation mode of the A-D converter.
(3)
Trigger select bit (bit 5 at address 1E16)
This bit is used to select the source of trigger occurrence. (Refer to section “(4) A-D conversion
start bit.”)
(4)
A-D conversion start bit (bit 6 at address 1E16)
s When internal trigger is selected
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 A-D conversion is
completed. In the repeat mode or repeat sweep mode, the A-D converter continues its operation
until this bit is cleared to “0” by software.
s When external trigger is selected
When pin ADTRG’s level changes from “H” to “L” (when the external trigger polarity select bit = “0”)
or from “L” to “H” (when the external trigger polarity select bit = “1”) with this bit = “1,” a trigger
is generated, causing the A-D converter to start its operation. The A-D converter halts when this
bit is cleared to “0.”
In the one-shot mode or single sweep mode, this bit remains set to “1” even after the A-D
conversion is completed. In the repeat mode or repeat sweep mode, the A-D converter continues
its operation until this bit is cleared to “0” by software.
(5) 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 13.2.1 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 during A-D conversion.
Table 13.2.1 Conversion time per one analog input pin
0
1
8-bit resolution mode
10-bit resolution mode
fsys = 26 MHz
Conversion time (
s) (Note)
φAD
0
1
0
1
f2 divided by 4
f2 divided by 2
f2
f1
15.08
7.54
3.77
1.88
A-D conversion
frequency (
φAD)
select bit 1
A-D conversion
frequency (
φAD)
select bit 0
Do not select.
Note: This applies when the peripheral devices’ clock select bit 0, 1 (bits 6, 7 at address BC16) = “002.”
18.15
9.07
4.54