gc80c520a CORERIVER Semiconductor, gc80c520a Datasheet - Page 47

• Manufacturer Part Number: gc80c520a
• Description: Midas1.0 Family Mask Rom/eprom/romless 8-bit Turbo Microcontrollers
• Manufacturer: CORERIVER Semiconductor

through the RxD. TxD outputs the shift clock. This mode, therefore, supports a half duplex mode of serial
communication. 8 bits are transmitted/received: 8 data bits (LSB first). Because the baud rate is fixed at
1/4 of the oscillator frequency, SM2 bit (SCON.5) should be 0 in mode 0.
The UART port sends and receives data through the RxD line. The TxD line outputs the shift clock. The
clock shifts data bits into and out of the devices at the either end of the line. Transmission is initiated by
any instruction that uses SBUF as a destination buffer. The shift clock will be activated and data will be
shifted out to the RxD pin until all 8 bits are transmitted. The data on RxD will appear four clock periods at
the center of the falling edge of TxD pin. This ensures that at the receiving end the data on RxD line can
either be clocked on the rising edge of the shift clock on TxD.
The TI flag is set high in S1 state following the end of transmission of the last bit. The UART port will
receive data when REN is 1 and RI is zero. The shift clock (TxD) will be activated and the serial port will
latch data at the low state of shift clock. The external device should therefore present data at the rising
edge on the shift clock. This process will be repeated until all the 8 bits have been received. The RI flag is
set in S1 state following the last rising edge of the shift clock on TxD. This will stop reception and hold
stop state until the RI is cleared by software.
MiDAS1.0 Family
REN
RI
S4
Write to
SBUF
Read SBUF
Load SBUF
Serial Port
Interrupt
Figure 6-18 UART Mode 0
D
CL
TB8
S
Q
START
TX CLOCK
RX CLOCK
START
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Internal BUS
Internal BUS
1 1 1 1 1 1 1 0
Input Shift Register
Zero Detector
RX CONTROL
TX CONTROL
SBUF
SBUF
TI
RI
SHIFT
RECEIVE
SHIFT
SEND
Shift
Clock
Shift
RXD
P3.0 ALT
OUTPUT
FUNCTION
RXD
P3.0 ALT
INPUT
FUNCTION
TXD
P3.1 ALT
OUTPUT
FUNCTION