M37544 RENESAS [Renesas Technology Corp], M37544 Datasheet - Page 61

• Manufacturer Part Number: M37544
• Description: SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
• Manufacturer: RENESAS [Renesas Technology Corp]

Rev.1.04
REJ03B0012-0104Z
7544 Group
Termination of Unused Pins
1. Terminate unused pins
Perform the following wiring at the shortest possible distance (20
mm or less) from microcomputer pins.
(1) I/O ports
Set the I/O ports for the input mode and connect each pin to V
or V
select a built-in pull-up resistor can also use the built-in pull-up re-
sistor.
When using the I/O ports as the output mode, open them at “L” or
“H”.
• When opening them in the output mode, the input mode of the
• Since the direction register setup may be changed because of a
2. Termination remarks
(1) I/O ports setting as input mode
[1] Do not open in the input mode.
<Reason>
[2] Do not connect to V
<Reason>
If the direction register setup changes for the output mode be-
cause of a program runaway or noise, a short circuit may occur.
[3] Do not connect multiple ports in a lump to V
<Reason>
If the direction register setup changes for the output mode be-
cause of a program runaway or noise, a short circuit may occur
between ports.
• The power source current may increase depending on the first-
• An effect due to noise may be easily produced as compared with
initial status remains until the mode of the ports is switched over
to the output mode by the program after reset. Thus, the poten-
tial at these pins is undefined and the power source current may
increase in the input mode. With regard to an effects on the sys-
tem, thoroughly perform system evaluation on the user side.
program runaway or noise, set direction registers by program
periodically to increase the reliability of program.
stage circuit.
proper termination (1) shown on the above “1. Terminate unused
pins”.
a resistor.
SS
through each resistor of 1 k
2004.06.08
CC
or V
page 61 of 66
SS
directly.
to 10 k . The port which can
CC
or V
SS
through
CC
Fig. 5 Sequence of changing relevant register
<Reason>
When setting the followings, the interrupt request bit of the corre-
sponding interrupt may be set to “1”.
• When switching external interrupt active edge
2. Check of interrupt request bit
When executing the BBC or BBS instruction to determine an in-
terrupt request bit immediately after this bit is set to “0”, take the
following sequence.
<Reason>
If the BBC or BBS instruction is executed immediately after an in-
terrupt request bit is cleared to “0”, the value of the interrupt
request bit before being cleared to “0” is read.
Fig. 6 Sequence of check of interrupt request bit
Notes on Interrupts
1. Change of relevant register settings
When not requiring for the interrupt occurrence synchronous with
the following case, take the sequence shown in Figure 5.
• When switching external interrupt active edge
• When switching interrupt sources of an interrupt vector address
INT
(bit 0 of Interrupt edge selection register (address 3A
INT
(bit 1 of Interrupt edge selection register)
CNTR
(bit 2 of timer X mode register (address 2B
CNTR
(bit 6 of timer A mode register (address 1D
where two or more interrupt sources are allocated
Set the interrupt edge selection bit, active edge switch bit, or
Set the corresponding interrupt enable bit to “0” (disabled) .
Set the corresponding interrupt enable bit to “1” (enabled).
0
1
Set the interrupt request bit to “0” (no interrupt issued)
interrupt edge selection bit
interrupt edge selection bit
0
1
Set the corresponding interrupt request bit to “0”
active edge switch bit
active edge switch bit
Execute the BBC or BBS instruction
the interrupt source selection bit.
NOP (One or more instructions)
NOP (one or more instructions)
(no interrupt request issued).
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