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Under
development
Preliminary Specifications REV.B3
Specifications in this manual are tentative and subject to change.
Mitsubishi Microcomputers
M32C/83 group
SINGLE-CHIP 16/32-BIT CMOS MICROCOMPUTER
Usage precaution
337
A-D Converter
(1) Write to each bit (except bit 6) of A-D i (i=0,1) control register 0, to each bit of A-D i control register 1,
and to each bit of A-D i control register 2 when A-D conversion is stopped (before a trigger occurs).
In particular, when the Vref connection bit is changed from “0” to “1”, start A-D conversion after an
elapse of 1
s or longer.
(2) When changing A-D operation mode, select analog input pin again.
(3) Using one-shot mode or single sweep mode
Read the correspondence A-D register after confirming A-D conversion is finished. (It is known by A-
D conversion interrupt request bit.)
(4) Using repeat mode, repeat sweep mode 0 or repeat sweep mode 1
Use the undivided main clock as the internal CPU clock.
(5) When f(XIN) is faster than 10 MHz, make the frequency 10 MHz or less by dividing.
(6) Output impedance of sensor at A-D conversion (Reference value)
To carry out A-D conversion properly, charging the internal capacitor C shown in Figure 1.31.1 has to
be completed within a specified period of time T. Let output impedance of sensor equivalent circuit be
R0, microcomputer’s internal resistance be R, precision (error) of the A-D converter be X, and the A-
D converter’s resolution be Y (Y is 1024 in the 10-bit mode, and 256 in the 8-bit mode).
Vc is generally VC = VIN {1 – e}
And when t = T,
VC=VIN –
VIN=VIN(1 –
)
e
=
–
=ln
Hence, R0 = –
– R
With the model shown in Figure 1.31.1 as an example, when the difference between VIN and VC becomes
0.1LSB, we find impedance R0 when voltage between pins VC changes from 0 to VIN-(0.1/1024) VIN in
time T. (0.1/1024) means that A-D precision drop due to insufficient capacitor charge is held to 0.1LSB at
time of A-D conversion in the 10-bit mode. Actual error however is the value of absolute precision added
to 0.1LSB. When f(XIN) = 10 MHz, T = 0.3
s in the A-D conversion mode with sample & hold. Output
impedance R0 for sufficiently charging capacitor C within time T is determined as follows.
T = 0.3
s, R = 7.8 k, C = 3 pF, X = 0.1, and Y = 1024 . Hence,
R0 = –– 7.8 X103
3.0 X 103
C (R0 +R)
T
C (R0 + R)
T
–
C (R0 + R)
t
–
Y
X
Y
X
Y
X
Y
X
C ln
T
Y
X
3.0 X 10 –12 ln
1024
0.1
0.3 X 10-6