31
38C2 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
PRELIMINARY
Notice: This is not a final specification.
Some parametric limits are subject to change.
(2) Asynchronous Serial I/O (UART) Mode
Clock asynchronous serial I/O mode (UART) can be selected by clear-
ing the serial I/O mode selection bit of the serial I/O control register
to
“
0
”
.
Eight serial data transfer formats can be selected, and the transfer
formats used by a transmitter and receiver must be identical.
The transmit and receive shift registers each have a buffer, but the
two buffers have the same address in memory. Since the shift regis-
ter cannot be written to or read from directly, transmit data is written
to the transmit buffer register, and receive data is read from the re-
ceive buffer register.
The transmit buffer register can also hold the next data to be trans-
mitted, and the receive buffer register can hold a character while the
next character is being received.
Fig. 27 Block diagram of UART serial I/O
f(X
IN
)
(f(X
CIN
) in low-speed mode)
1/4
OE
PE FE
1/16
1/16
Data bus
Receive buffer register
Receive shift register
Receive buffer full flag (RBF)
Receive interrupt request (RI)
Baud rate generator
Address 0FE2
16
[Address 0FE5
16
]
Frequency division ratio 1/(n+1)
ST/SP/PA generator
Transmit buffer register
Address 001C
16
[Address 001E
16
]
Data bus
Transmit shift register
Transmit shift completion flag (TSC)
Transmit buffer empty flag (TBE)
Serial I/O status register
Transmit interrupt request (TI)
ST detector
SP detector
UART control register
Address 0FE1
16
[Address 0FE4
16
]
Character length selection bit
BRG count source selection bit
Transmit interrupt source selection bit
Serial I/O synchronous clock selection bit
Clock control circuit
Character length selection bit
7 bits
8 bits
Serial I/O control register
P5
6
/S
CLK1
[P3
1
/S
CLK2
]
P5
4
/R
X
D
1
[P3
3
/R
X
D
2
]
P5
5
/T
X
D
1
[P3
2
/T
X
D
2
]
Address 001C
16
[Address 001E
16
]
Address 001D
16
[Address 001F
16
]
Address 0FE0
16
[Address 0FE3
16
]
[ ] : For Serial I/O2
Fig. 28 Operation of UART serial I/O function
TSC=0
TBE=1
RBF=0
TBE=0
TBE=0
RBF=1
RBF=1
ST
D
0
D
1
SP
D
0
D
1
ST
SP
TBE=1
TSC=1
ST
D
0
D
1
SP
D
0
D
1
ST
SP
Transmit or receive clock
Transmit buffer write
signal
Generated at 2nd bit in 2-stop-bit mode
1 start bit
7 or 8 data bit
1 or 0 parity bit
1 or 2 stop bit (s)
1:
Error flag detection occurs at the same time that the RBF flag becomes
“
1
”
(at 1st stop bit, during reception).
2:
As the transmit interrupt (TI), when either the TBE or TSC flag becomes
“
1,
”
can be selected to occur depending on the setting of the transmit
interrupt source selection bit (TIC) of the serial I/O control register.
3:
The receive interrupt (RI) is set when the RBF flag becomes
“
1.
”
4:
After data is written to the transmit buffer when TSC=1, 0.5 to 1.5 cycles of the data shift cycle is necessary until changing to TSC=0.
Notes
Serial output T
X
D
Serial input R
X
D
Receive buffer read
signal