W78E052DDG Nuvoton Technology Corporation of America, W78E052DDG Datasheet - Page 57

• Manufacturer Part Number: W78E052DDG
• Description: IC MCU 8-BIT 8K FLASH 40-DIP
• Manufacturer: Nuvoton Technology Corporation of America
• Series: W78r

Specifications of W78E052DDG

• Core Processor: 8052
• Core Size: 8-Bit
• Speed: 40MHz
• Connectivity: EBI/EMI, UART/USART
• Peripherals: POR, WDT
• Number Of I /o: 36
• Program Memory Size: 8KB (8K x 8)
• Program Memory Type: FLASH
• Ram Size: 256 x 8
• Voltage - Supply (vcc/vdd): 2.4 V ~ 5.5 V
• Oscillator Type: External
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 40-DIP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Data Converters: -

W78E054D/W78E052D/W78E051D Data Sheet
16 SERIAL PORT
Serial port in this device is a full duplex port. The serial port is capable of synchronous as well as
asynchronous communication. In Synchronous mode the device generates the clock and operates in a
half duplex mode. In the asynchronous mode, full duplex operation is available. This means that it can
simultaneously transmit and receive data. The transmit register and the receive buffer are both ad-
dressed as SBUF Special Function Register. However any write to SBUF will be to the transmit regis-
ter, while a read from SBUF will be from the receiver buffer register. The serial port can operate in four
different modes as described below.
16.1 MODE 0
This mode provides synchronous communication with external devices. In this mode serial data is
transmitted and received on the RXD line. TXD is used to transmit the shift clock. The TxD clock is
provided by the device whether it is transmitting or receiving. This mode is therefore a half duplex
mode of serial communication. In this mode, 8 bits are transmitted or received per frame. The LSB is
transmitted/received first. The baud rate is fixed at 1/12 of the oscillator frequency. This Baud Rate is
determined by the SM2 bit (SCON.5). When this bit is set to 0, then the serial port runs at 1/12 of the
clock. This additional facility of programmable baud rate in mode 0 is the only difference between the
standard 8051 and W78E054D/W78E052D/W78E051D.
The functional block diagram is shown below. Data enters and leaves the Serial port on the RxD line.
The TxD line is used to output the shift clock. The shift clock is used to shift data into and out of this
device and the device at the other end of the line. Any instruction that causes a write to SBUF will start
the transmission. The shift clock will be activated and data will be shifted out on the RxD pin till all 8
bits are transmitted. If SM2 = 1, then the data on RxD will appear 1 clock period before the falling
edge of shift clock on TxD. The clock on TxD then remains low for 2 clock periods, and then goes high
again. If SM2 = 0, the data on RxD will appear 3 clock periods before the falling edge of shift clock on
TxD. The clock on TxD then remains low for 6 clock periods, and then goes high again. 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 or latched when the TxD clock is low.
Publication Release Date: Dec 29, 2009
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Revision A09