7220 Datasheet, PDF (229/303 Pages) Renesas Technology Corp – 8-BIT SINGLE-CHIP MICROCOMPUTER

APPENDIX
6.3 Notes on use
6.3.10 Note on multi-master I²C-BUS interface
This function is used at f(XIN) = 8.0 MHz of oscillation frequency.
6.3.11 Termination of unused pins
(1) Proper termination of unused pins
s Output ports : Open
s Input ports :
Connect each pin to VCC or VSS through each resistor of 1 kW to 10 kW.
Ports that permit the selecting of a built-in pull-up or pull-down resistor can also use this resistor.
As for pins whose potential affects to operation modes such as pins CNVSS, INT or others, select
the VCC pin or the VSS pin according to their operation mode.
s I/O ports :
•Set the I/O ports for the input mode and connect them to VCC or VSS through each resistor of
1 kΩ to 10 kΩ. Set the I/O ports for the output mode and open them at “L” or “H.”
•When opening them in the output mode, the input mode of the initial status remains until the mode
of the ports is switched over to the output mode by the program after reset. Thus, the potential
at these pins is undefined and the power source current may increase in the input mode. With
regard to an effects on the system, thoroughly perform system evaluation on the user side.
•Since the direction register setup may be changed because of a program runaway or noise, set
direction registers by program periodically to increase the reliability.
(2) Incorrect termination of unused pins
s input ports and I/O ports :
Do not open in the input mode.
Reason
•The power supply current may increase depending on the first-stage circuit.
•An effect due to noise may be easily produced as compared with proper termination (1).
shown on the above.
s I/O ports :
Set for input mode and do not connect to VCC or VSS directly.
Reason
If the direction register setup changes for the output mode because of a program runaway or
noise, a short circuit may occur between a port and VCC (or VSS).
s I/O ports :
Set for the input mode and do not connect multiple ports in a lump to VCC or VSS through a resistor.
Reason
If the direction register setup changes for the output mode because of a program runaway or
noise, a short circuit may occur between ports.
(3) At the termination of unused pins, perform wiring at the shortest possible distance (20 mm or
less) from microcomputer pins.
6-10
7220 Group User’s Manual