A-D CONVE R T E R
7751 Group User’s Manual
8–5
(2)
Trigger select bit (bit 5)
This bit is used to select the source of trigger occurrence. (Refer to
“(3) A-D conversion start bit.”
)
(3)
A-D conversion start bit (bit 6)
G
When internal trigger is selected
Setting this bit to “1” generates a trigger, causing the A-D converter to start operating. Clearing
this bit to “0” causes the A-D converter to stop operating.
In the one-shot mode or single sweep mode, this bit is cleared to “0” after the operation is
completed. In the repeat mode, repeat sweep mode 0 or repeat sweep mode 1, the A-D converter
continues operating until this bit is cleared to “0” by software.
G
When external trigger is selected
When the
AD
TRG
pin level goes from “H” to “L” with this bit = “1,” a trigger occurs, causing the
A-D converter to start operating. The A-D converter stops 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 operation
is completed. In the repeat mode, repeat sweep mode 0 or repeat sweep mode 1, the A-D
converter continues operating until this bit is cleared to “0” by software.
(4)
A-D conversion frequency (
φ
AD
) select bit 0 (bit 7)
The operating time of the A-D converter varies depending on the selected operating clock (
φ
AD
) by
this bit and the A-D conversion frequency (
φ
AD
) select bit 1 (bit 4 at address 1F
16
; refer to Figure
8.2.3) as listed in Table 8.2.3.
Since the A-D converter’s comparator consists of capacity coupling amplifiers, keep that
φ
AD
≥
250
kHz during A-D conversion
.
8.2 Block description
Table 8.2.1 Time for performance to one analog input pin (unit: μs)
Clock source for peripheral devices select bit
A-D conversion frequency (
φ
AD
) select bit 1
A-D conversion frequency (
φ
AD
) select bit 0
φ
AD
f
4
divided by 4
8-bit resolution
10-bit resolution
8-bit resolution
10-bit resolution
f(X
IN
) = 25 MHz
f(X
IN
) = 40 MHz
0
0
31.36
37.76
19.60
23.60
0
1
f
4
divided by 2
15.68
18.88
9.80
11.80
1
0
f
4
7.84
9.44
4.90
5.90
0
1
f
2
divided by 2
7.84
9.44
–––
–––
1
0
f
2
3.92
4.72
–––
–––
0
0
f
2
divided by 4
15.68
18.88
–––
–––
0
1