AS8218 datasheet(107/123 Pages) AMSCO

107 / 123 page

Data Sheet AS8218 / AS8228

Revision 3.0, 31-May-06

Page 107 of 123

Bit

Symbol Function

Mode

Bit7

Bit6

Mode 0: same as Mode 1, (Mode 0 is not implemented due to

standard 8051)

SM0

Mode 1: 8-bit UART1, variable Baudrate. - The serial transmission

is set to 8 data bits. However up to 10 bits can be sent at port

TxD

and received at port

RxD: start bit (always ‘0’), eight data bits (LSB

first), and a stop bit (always ‘1’). The value of a received stop bit is

transferred to SCON.RB8 and can be evaluated by the software.

Mode 2: 9-bit UART1, variable Baudrate. - The serial transmission

is set to 9 data bits. However up to 11 bits can be sent at port

TxD

and received at port

RxD: start bit (always ‘0’), nine data bits (LSB

first), and a stop bit (always ‘1’). The value of SCON.TB8 is used

for transmitting the ninth data bit (usually as parity bit). The value

of the received ninth data bit is transferred to SCON.RB8 and can

be evaluated by the software.

SM1

Mode select

flags

Mode 3: 9-bit UART1, variable Baudrate. – same as Mode 2.

SM2

Mode Select Flag 2: Enables the multiprocessor communications feature in Mode 2.

Mode 0: SM2 is not used.

Mode 1: When SM2=’1’, RI is not set and SBUF is not loaded if the received stop bit is ‘0’.

Mode 2: When SM2=’1’, RI is not set and SBUF is not loaded if the received ninth data bit is ‘0’. Please

refer also to section Multiprocessor Communications.

REN

Receiver Enable Flag. With REN=’0’ the receiver is disabled, otherwise enabled. REN is to be set and

cleared by the software.

TB8

Value of the ninth data bit to be sent when in mode 2.

RB8

Value of the ninth data bit received when in mode 2 or value of the stop bit received when in mode 1.

Not used in mode 0.

Transmit Interrupt Flag. This flag is set by the UART1 at the end of transmitting. In mode 0 flag TI is set

at the end of the eighth data bit, in all others modes at the beginning of the stop bit. Flag TI must be

cleared by the software.

Receive Interrupt Flag. This flag is set by the hardware at the end of receiving. In mode 0 flag RI is set

at the end of the eighth data bit, in mode 1 at the middle of the stop bit, and in mode 2 at the middle of

the ninth data bit. Flag RI must be cleared by the software.

Note:

1) Mode Select Flags 0/1: These bits are used to select one of four transmission modes. In all four modes the

baudrate is determined by the Baudrate Generator.

SBUF Registers

The 8-bit register SBUF is the data buffer register which actually consists of two registers for both transmitting

and receiving data. Both are accessed by the same address SBUF. A write access to SBUF is redirected into

the internal register TransmitSBUF, a read access to SBUF is redirected to the internal register ReceiveSBUF.

Remark: The (optional) ninth data bit is defined in SCON.TB8/RB8.

SBUF

MSB

LSB

Data 7

Data 6

Data 5

Data 4

Data 3

Data 2

Data 1

Data 0

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