M37754 Mitsubishi, M37754 Datasheet - Page 55

• Manufacturer Part Number: M37754
• Description: SINGLE-CHIP 16BIT CMOS MICROCOMPUTER
• Manufacturer: Mitsubishi

Receive
Receive is enabled when bit 2 (REi flag) of UARTi Transmit/Receive
control register 1 is set to “1.” As shown in Figure 67, the frequency
divider circuit (1/16) at the receiving side begin to work when a start
bit arrives and the data is received.
If RTSi output is selected by setting bit 2 of UARTi Transmit/Receive
control register 0 to “1”, the RTSi output is “H” when the REi flag is
“0”. When the REi flag changes to “1”, the RTSi output goes “L” to
indicate receive ready and returns to “H” once receive has started. In
other words, RTSi output can be used to determine externally
whether the receive register is ready to receive.
The entire transmission data bits are received when the start bit
passes the final bit of the receive block shown in Figure 56. At this
point, the contents of the receive register is transferred to the receive
buffer register and bit 3 (Rli flag) of UARTi Transmit/Receive control
register 1 is set to “1.” In other words, the RIi flag indicates that the
receive buffer register contains data when it is set to “1.” If RTSi out-
put is selected, RTSi output goes “L” to indicate that the register is
ready to receive the next data.
The interrupt request bit of the UARTi receive interrupt control regis-
ter is set to “1” when the RIi flag changes from “0” to “1”.
Bit 4 (OERi flag) of UARTi Transmit/Receive control register 1 is set
to “1” when the next data is transferred from the receive register to
the receive buffer register while the RIi flag is “1”, in other words,
when an overrun error occurs. If the OERi flag is “1”,
it indicates that the next data has been transferred to the receive
buffer register before the contents of the receive buffer register has
been read.
Bit 5 (FERi flag) is set to “1” when the number of stop bits is less than
required (framing error).
Bit 6 (PERi flag) is set to “1” when a parity error occurs.
Bit 7 (SUMi flag) is set to “1” when either the OERi flag, FERi flag, or
the PERi flag is set to “1.” Therefore, the SUMi flag can be used to
determine whether there is an error.
The setting of the RIi flag, OERi flag, FERi flag, and the PERi flag is
performed while transferring the contents of the receive register to
the receive buffer register. The Rli, FERi, and PERi flags are cleared
Fig. 67 Receive timing example when 8-bit asynchronous communication with no parity and 1 stop bit selected
____
Pf
RE
R
Receive
Clock
RI
RTS
X
i
i
D
or f
i
i
i
EXT
____
____
Starting at the falling
edge of start bit
____
Start bit
____
Check to be “L” level
M37754M8C-XXXGP, M37754M8C-XXXHP
____
D
0
Data fetched
to “0” when reading the low-order byte of the receive buffer register
or when writing “0” to the REi flag or when setting to a parallel port.
The OERi and SUMi flags are cleared to “0” when writing “0” to the
REi flag or when setting to a parallel port.
The SUMi flag is cleared to “0” when the OERi, FERi, PERi flags are
cleared to “0” all.
Sleep mode
The sleep mode is used to communicate only between certain micro-
computers when multiple microcomputers are connected through se-
rial I/O.
The microcomputer enters the sleep mode when bit 7 of UARTi
Transmit/Receive mode register is set to “1.”
The operation of the sleep mode for an 8-bit asynchronous commu-
nication is described below.
When sleep mode is selected, the contents of the receive register is
not transferred to the receive buffer register if bit 7 (bit 6 if 7-bit asyn-
chronous communication and bit 8 if 9-bit asynchronous communica-
tion) of the received data is “0”. Also the RIi, OERi, FERi, PERi, and
the SUMi flag are unchanged. Therefore, the interrupt request bit of
the UARTi receive interrupt control register is also unchanged. Nor-
mal receive operation takes place when bit 7 of the received data is
“1”.
The following is an example of how the sleep mode can be used.
The main microcomputer first sends data: bit 7 is “1” and bits 0 to 6
are set to the address of the subordinate microcomputer to be com-
municated with. Then all subordinate microcomputers receive this
data. Each subordinate microcomputer checks the received data,
clears the sleep bit to “0” if bits 0 to 6 are its own address and sets
the sleep bit to “1” if not. Next, the main microcomputer sends data
with bit 7 cleared. Then the microcomputer which cleared the sleep
bit will receive the data, but the microcomputers which set the sleep
bit to “1” will not. In this way, the main microcomputer is able to com-
municate only with the designated microcomputer.
M37754S4CGP, M37754S4CHP
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
D
1
MITSUBISHI MICROCOMPUTERS
D
7
Stop bit
Start bit
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