
33
38C2 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
PRELIMINAR
Y
Notice:
This
is not
a final
specification.
Some
parametric
limits
are
subject
to change.
[Transmit Buffer Register/Receive Buffer Reg-
ister (TB/RB)]
The transmit buffer register and the receive buffer register are lo-
cated at the same address. The transmit buffer is write-only and the
receive buffer is read-only. If a character bit length is 7 bits, the MSB
of data stored in the receive buffer is “0”.
[Serial I/O Status Register (SIO1STS, SIO2STS)]
The read-only serial I/O status register consists of seven flags (bits 0
to 6) which indicate the operating status of the serial I/O function and
various errors.
Three of the flags (bits 4 to 6) are valid only in UART mode.
The receive buffer full flag (bit 1) is cleared to “0” when the receive
buffer register is read.
If there is an error, it is detected at the same time that data is trans-
ferred from the receive shift register to the receive buffer register,
and the receive buffer full flag is set. A write to the serial I/O status
register clears all the error flags OE, PE, FE, and SE (bit 3 to bit 6,
respectively). Writing “0” to the serial I/O enable bit SIOE (bit 7 of the
serial I/O control register) also clears all the status flags, including
the error flags.
All bits of the serial I/O status register are initialized to “0” at reset,
but if the transmit enable bit (bit 4) of the serial I/O control register
has been set to “1”, the transmit shift completion flag (bit 2) and the
transmit buffer empty flag (bit 0) become “1”.
[Serial I/O Control Register (SIO1CON, SIO2CON)]
The serial I/O control register consists of eight control bits for the
serial I/O function.
[UART Control Register (UART1CON, UART2CON)]
The UART control register consists of four control bits (bits 0 to 3)
which are valid when asynchronous serial I/O is selected and set the
data format of an data transfer and one bit (bit 4) which is always
valid and sets the output structure of the P55/TXD1 [P32/TxD2] pin.
[Baud Rate Generator (BRG1, BRG2)]
The baud rate generator determines the baud rate for serial transfer.
The baud rate generator divides the frequency of the count source
by 1/(n + 1), where n is the value written to the baud rate generator.