HT45B0F

Rev. 1.00

7

June 7, 2011

UART Commands

There are both read and write commands. For reading and writing to registers both command and address information

is contained within a single byte. The format for reading and writing is shown in the following table.

Command Type

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Read FIFO

00000

X

X

X

Read Register

00010

A2

A1

A0

Write FIFO

00001

X

X

X

Write Register

00011

A2

A1

A0

Note:

²X² here stands for ²don¢t care²

UART Status and Control Registers

There are six registers associated with the UART function. The USR, UCR1, UCR2 and UCR3 registers control the

overall function, while the BRG register controls the Baud rate. The actual data to be transmitted and received on the

serial interface is managed through the TXR/RXR data register.

A[2:0]

Name

Reset

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

00H

USR

0000 1011

PERR

NF

FERR

OERR

RIDLE

RXIF

TIDLE

TXIF

01H

UCR1

0000 0X00

UARTEN

BNO

PREN

PRT

STOPS

TXBRK

RX8

TX8

02H

UCR2

0000 0000

TXEN

RXEN

BRGH

ADDEN

WAKE

RIE

TIIE

TEIE

03H

BRG

XXXX XXXX

BRG7

BRG6

BRG5

BRG4

BRG3

BRG2

BRG1

BRG0

04H

UCR3

0

--- ----

URST

¾

¾¾¾¾¾

¾

05H~

07H

Unused

---- ----

Reserved

UART Register Summary

The USR register is the status register for the UART, which can be read by the application program to determine the

present status of the UART. All flags within the USR register are read only. Further explanation on each of the flags is

given below:

Bit

76543210

Name

PERR

NF

FERR

OERR

RIDLE

RXIF

TIDLE

TXIF

R/W

RRRRRRRR

POR

00001011

Bit 7

PERR: Parity error flag

0: no parity error is detected

1: parity error is detected

The PERR flag is the parity error flag. When this read only flag is

²0², it indicates a parity error

has not been detected. When the flag is

²1², it indicates that the parity of the received word is

incorrect. This error flag is applicable only if Parity mode (odd or even) is selected. The flag can

also be cleared by a software sequence which involves a read to the status register USR

followed by an access to the RXR data register.

Bit 6

NF: Noise flag

0: no noise is detected

1: noise is detected

The NR flag is the noise flag. When this read only flag is

²0², it indicates no noise condition.

When the flag is

²1², it indicates that the UART has detected noise on the receiver input.

The NF flag is set during the same cycle as the RXIF flag but will not be set in the case of as

overrun. The NF flag can be cleared by a software sequence which will involve a read to the

status register USR followed by an access to the RXR data register.