Analog Devices ADuC812 - Manual (Page 35)

REV. B
ADuC812
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UART SERIAL INTERFACE
The serial port is full duplex, meaning it can transmit and receive
simultaneously. It is also receive-buffered, meaning it can com-
mence reception of a second byte before a previously received byte
has been read from the receive register. However, if the first
byte still has not been read by the time reception of the second
byte is complete, the first byte will be lost. The physical inter-
face to the serial data network is via Pins RXD(P3.0) and
TXD(P3.1) while the SFR interface to the UART is comprised
of SBUF and SCON, as described below.
SBUF
The serial port receive and transmit registers are both accessed
through the SBUF SFR (SFR address = 99 hex). Writing to
SBUF loads the transmit register and reading SBUF accesses a
physically separate receive register.
SCON UART Serial Port Control
Register
SFR Address 98H
Power-On Default Value 00H
Bit Addressable Yes
0 M S 1 M S 2 M S N E R 8 B T 8 B R I T I R
Table XX. SCON SFR Bit Designations
Bit Name Description
7 SM0 UART Serial Mode Select Bits.
6 SM1 These bits select the Serial Port operating mode as follows:
SM0
SM1 Selected Operating Mode
0 0 Mode 0: Shift Register, fixed baud rate (Core_Clk/2)
0 1 Mode 1: 8-bit UART, variable baud rate
1 0 Mode 2: 9-bit UART, fixed baud rate (Core_Clk/64) or
(Core_Clk/32)
1 1 Mode 3: 9-bit UART, variable baud rate
5 SM2 Multiprocessor Communication Enable Bit.
Enables multiprocessor communication in Modes 2 and 3. In Mode 0, SM2 should be cleared.
In Mode 1, if SM2 is set, RI will not be activated if a valid stop bit was not received. If SM2 is
cleared, RI will be set as soon as the byte of data has been received. In Modes 2 or 3, if SM2 is
set, RI will not be activated if the received ninth data bit in RB8 is 0. If SM2 is cleared, RI will
be set as soon as the byte of data has been received.
4 REN Serial Port Receive Enable Bit.
Set by user software to enable serial port reception.
Cleared by user software to disable serial port reception.
3 TB8 Serial Port Transmit (Bit 9).
The data loaded into TB8 will be the ninth data bit that will be transmitted in Modes 2 and 3.
2 RB8 Serial port Receiver Bit 9.
The ninth data bit received in Modes 2 and 3 is latched into RB8. For Mode 1 the stop bit is
latched into RB8.
1 TI Serial Port Transmit Interrupt Flag.
Set by hardware at the end of the eighth bit in Mode 0, or at the beginning of the stop bit in
Modes 1, 2, and 3. TI must be cleared by user software.
0 RI Serial Port Receive Interrupt Flag.
Set by hardware at the end of the eighth bit in mode 0, or halfway through the stop bit in
Modes 1, 2, and 3. RI must be cleared by software.