H83724 Datasheet, PDF (71/352 Pages) Renesas Technology Corp – Renesas 8-Bit Single-Chip Microcomputer H8 Family/H8/300L Series

As noted above, the H8/300L CPU executes bit manipulation instructions 8 bits at a time, in the
order read → modify → write. Since the same address is used for the I/O port data register and
the read portion of pin input, a bit manipulation instruction designating a port functions as
follows.
x High-voltage pin: pin other than the modified bit
• When set as an input pin (data register = 0)
First the CPU reads the pin input level (read), then it sets or resets the designated bit
(modify; other bits remain the same), and writes that value to the data register (write). If
the input level is high (read data = 1), a value of 1 is written to the data register, changing
the input pin to an output pin (high-level output). If the input level is low, no change
occurs.
• When set as an output pin (data register = 1, high-level output)
If the output level is higher than the input high level (V_IH), there is no change.
If the output level is lower than the input low level (V_IL), a value of 0 is written to the data
register, so that the PMOS buffer is turned off resulting in pull-down (low level) or high-
impedance state.
If a load is applied so that the output level is pulled down to a medium level, the resulting
state is indeterminate.
y Standard-voltage pin: pin other than the modified bit
• When set as an input pin
The CPU reads the pin input level and writes that value to the data register, which may or
may not result in a change to the data register contents.
• When set as an output pin
The data register is read, so no change occurs.
2. Bit manipulation in a register containing a write-only bit
Example: PWM data register, etc.
(Note that read and write characteristics can differ from bit to bit.)
In this case there is no register (on the source side) to be read, so a bit other than the designated bit
takes a value of 1.
Rev. 3.00, 12/94, page 56 of 334