MITSUBISHI MICROCOMPUTERS
7477/7478 GROUP
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
A-D CONVERTER
The A-D conversion register (address 00DA16) contains informa-
tion on the results of conversion, so that it is possible to know the
results of conversion by reading the contents of this register.
The following explains the procedure to execute A-D conversion.
First, set values to bit 2 to bit 0 in the A-D control register to select
the pins that you want to execute A-D conversion. Next, clear the
A-D conversion end bit to “0”. When the above is done, A-D con-
version is initiated. The A-D conversion is completed after an
elapse of 50 machine cycles (12.5µs when f(XIN) = 8MHz), the A-
D conversion end bit is set to “1”, and the interrupt request bit is
set to “1”. The results of conversion are contained in the A-D con-
version register.
The A-D conversion uses an 8-bit successive comparison method.
Figure 13 shows a block diagram of the A-D conversion circuit.
Conversion is automatically carried out once started by the pro-
gram.
There are eight analog input pins which are shared with P20 to
P27 of port P2 (Only P20 to P23 4-bit for 7477 group).
Which analog inputs are to be A-D converted is specified by using
bit 2 to bit 0 in the A-D control register (address 00D916). Pins for
inputs to be A-D converted must be set for input by setting the di-
rection register bit to “0”. Bit 3 in the A-D control register is an A-D
conversion end bit. This is “0” during A-D conversion; it is set to “1“
when the conversion is terminated. Therefore, it is possible to
know whether A-D conversion is terminated by checking this bit.
Figure 14 shows the relationship between the contents of A-D
control register and the selected input pins.
Data bus
bit 3
bit 0
A-D control register
(address 00D916)
A-D conversion
completion
interrupt request
P20/IN0
P21/IN1
P22/IN2
P23/IN3
P24/IN4
P25/IN5
P26/IN6
P27/IN7
A-D control circuit
A-D conversion register
(address 00DA16)
Comparator
Switch tree
Ladder resistor
VSS (Note 1)
VREF
Notes 1 : AVSS for M37478M4/M8/E8-XXXFP.
2 : The 7477 group does not have P2 4/IN4 to P27/IN7 pins.
Fig. 13 A-D converter circuit
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MITSUBISHI [ Mitsubishi Group ]
