6MPS5 datasheet(65/101 Pages) TI1

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The UnTBE flag is automatically reset by the USART when

the software loads a new character into the UnTBUF register.

During transmission, the UnXMIP bit is set high by the

USART. This bit is reset only after the USART has sent the

last frame bit of the current character and the UnTBUF regis-

ter is empty.

The receive shift register (RSFT) and the receive buffer

(UnRBUF) double-buffer the data being received. Serial data

received on the RDXn pin is shifted into the RSFT register at

the first falling edge of the clock. Each subsequent falling

edge of the clock causes an additional bit to be shifted into

the RSFT register. The USART assumes a complete charac-

ter has been received after the correct number of rising edg-

es on CKXn (based on the selected frame format) have been

detected. Upon receiving a complete character, the contents

of the RSFT register are copied into the UnRBUF register

and the Receive Buffer Full flag (UnRBF) is set. The UnRBF

flag is automatically reset when the software reads the char-

acter from the UnRBUF register.

The transmitter and receiver may be clocked from either an

external source provided to the CKXn pin or by the internal

baud rate generator. In the latter case, the clock signal is

placed on the CKXn pin as an output.

16.2.3

Attention Mode

The Attention mode is available for networking this device

with other processors. This mode requires the 9-bit data for-

mat with no parity. The number of start bits and number of

stop bits are programmable. In this mode, two types of 9-bit

characters are sent on the network: address characters con-

sisting of 8 address bits and a 1 in the ninth bit position and

data characters consisting of 8 data bits and a 0 in the ninth

bit position.

While in Attention mode, the USART receiver monitors the

communication flow but ignores all characters until an ad-

dress character is received. Upon the receipt of an address

character, the contents of the receive shift register are copied

to the receive buffer. The UnRBF flag is set and an interrupt

(if enabled) is generated. The UnATN bit is automatically re-

set to zero, and the USART begins receiving all subsequent

characters. The software must examine the contents of the

UnRBUF register and respond by accepting the subsequent

characters (by leaving the UnATN bit reset) or waiting for the

next address character (by setting the UnATN bit again).

The operation of the USART transmitter is not affected by the

selection of this mode. The value of the ninth bit to be trans-

mitted is programmed by setting or clearing a bit called

UnXB9 in the USART Frame Select Register. The value of

the ninth bit received is read from another register bit called

UnRB9 in the USART Status Register.

16.2.4

Diagnostic Mode

The Diagnostic mode is available for testing of the USART. In

this mode, the TDXn and RDXn pins are internally connected

together, and data that is shifted out of the transmit shift reg-

ister is immediately transferred to the receive shift register.

This mode supports only the 9-bit data format with no parity.

The number of start and stop bits is programmable.

16.2.5

Frame Format Selection

The format shown in Figure29 consists of a start bit, seven

data bits (excluding parity), and one or two stop bits. If parity

bit generation is enabled by setting the UnPEN bit, a parity

bit is generated and transmitted following the seven data bits.

The format shown in Figure30 consists of one start bit, eight

data bits (excluding parity), and one or two stop bits. If parity

bit generation is enabled by setting the UnPEN bit, a parity

bit is generated and transmitted following the eight data bits.

The format shown in Figure31 consists of one start bit, nine

data bits, and one or two stop bits. This format also supports

the USART attention feature. When operating in this format,

all eight bits of UnTBUF and UnRBUF are used for data. The

ninth data bit is transmitted and received using two bits in the

control registers, called UnXB9 and UnRB9. Parity is not

generated or verified in this mode.

16.2.6

Baud Rate Generator

The Baud Rate Generator creates the basic baud clock from

the system clock. The system clock is passed through a two-

Figure 28.

USART Synchronous Communication

CKX

TDX

RDX

Sample Input

Figure 29.

Seven Data Bit Frame Options

Figure 30.

Eight Data Bit Frame Options

START

BIT

7 BIT DATA

START

BIT

7 BIT DATA

START

BIT

7 BIT DATA

START

BIT

7 BIT DATA

START

BIT

8 BIT DATA

START

BIT

8 BIT DATA

START

BIT

8 BIT DATA

START

BIT

8 BIT DATA

CR16MNS5, CR16MFS5, and CR16MPS5 are Obsolete Devices

6MPS5 Datasheet(PDF) 65 Page - Texas Instruments

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