3803L Datasheet, PDF (95/119 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

3803 Group (Spec.L)
NOTES ON PERIPHERAL FUNCTIONS
Notes on Input and Output Ports
1. Notes in standby state
In standby state^*1 for low-power dissipation, do not make input
levels of an I/O port “undefined”. Even when an I/O port of
Nchannel open-drain is set as output mode, if output data is “1”,
the aforementioned notes are necessary.
Pull-up (connect the port to VCC) or pull-down (connect the port
to VSS) these ports through a resistor.
When determining a resistance value, note the following points:
• External circuit
• Variation of output levels during the ordinary operation
When using built-in pull-up resistor, note on varied current
values:
• When setting as an input port : Fix its input level
• When setting as an output port : Prevent current from flowing
out to external
<Reason>
Exclusive input ports are always in a high-impedance state. An
output transistor becomes an OFF state when an I/O port is set as
input mode by the direction register, so that the port enter a
highimpedance state. At this time, the potential which is input to
the input buffer in a microcomputer is unstable in the state that
input levels are “undefined”. This may cause power source
current.
Even when an I/O port of N-channel open-drain is set as output
mode by the direction register, if the contents of the port latch is
“1”, the same phenomenon as that of an input port will occur.
*1 _{Standby state : stop mode by executing STP instruction}
wait mode by executing WIT instruction
2. Modifying output data with bit managing instruction
When the port latch of an I/O port is modified with the bit
managing instruction^*1, the value of the unspecified bit may be
changed.
<Reason>
I/O ports are set to input or output mode in bit units. Reading
from a port register or writing to it involves the following
operations.
• Port in input mode
Read: Read the pin level.
Write: Write to the port latch.
• Port in output mode
Read: Read the port latch or read the output from the peripheral
function (specifications differ depending on the port).
Write: Write to the port latch. (The port latch value is output
from the pin.)
Since bit managing instructions^*1 are read-modify-write
instructions,^*2 using such an instruction on a port register causes
a read and write to be performed simultaneously on the bits other
than the one specified by the instruction.
When an unspecified bit is in input mode, its pin level is read and
that value is written to the port latch. If the previous value of the
port latch differs from the pin level, the port latch value is changed.
If an unspecified bit is in output mode, the port latch is generally
read. However, for some ports the peripheral function output is
read, and the value is written to the port latch. In this case, if the
previous value of the port latch differs from the peripheral
function output, the port latch value is changed.
Termination of Unused Pins
1. Terminate unused pins
(1) Output ports : Open
(2) 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.
Ports that permit the selecting of a built-in pull-up resistor can
also use this resistor. 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 of program.
(3) The AVSS pin when not using the A/D converter :
• When not using the A/D converter, handle a power source pin
for the A/D converter, AVSS pin as follows:
AVSS: Connect to the VSS pin.
2. Termination remarks
(1) I/O ports :
Do not open in the input mode.
<Reason>
• The power source current may increase depending on the
firststage circuit.
• An effect due to noise may be easily produced as compared
with proper termination (2) in 1 and shown on the above.
(2) I/O ports :
When setting for the input mode, 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).
(3) I/O ports :
When setting for the input mode, 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.
• At the termination of unused pins, perform wiring at the
shortest possible distance (20 mm or less) from micro-
computer pins.
*1 _{Bit managing instructions: SEB and CLB instructions}
*2 _{Read-modify-write instructions: Instructions that read memory}
in byte units, modify the value, and then write the result to the
same location in memory in byte units
Rev.1.01 Jan 25, 2008 Page 95 of 117
REJ03B0212-0101