PIC17C44 datasheet(83/241 Pages) MICROCHIP

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DS30412C-page 83

PIC17C4X

13.0

UNIVERSAL SYNCHRONOUS

ASYNCHRONOUS RECEIVER

TRANSMITTER (USART)

MODULE

The USART module is a serial I/O module. The USART

can be conﬁgured as a full duplex asynchronous sys-

tem that can communicate with peripheral devices such

as CRT terminals and personal computers, or it can be

conﬁgured as a half duplex synchronous system that

can communicate with peripheral devices such as A/D

or D/A integrated circuits, Serial EEPROMs etc. The

USART can be conﬁgured in the following modes:

• Asynchronous (full duplex)

• Synchronous - Master (half duplex)

• Synchronous - Slave (half duplex)

The SPEN (RCSTA<7>) bit has to be set in order to

conﬁgure RA4 and RA5 as the Serial Communication

Interface.

The USART module will control the direction of the

RA4/RX/DT and RA5/TX/CK pins, depending on the

states of the USART conﬁguration bits in the RCSTA

and TXSTA registers. The bits that control I/O direction

are:

• SPEN

• TXEN

• SREN

• CREN

• CSRC

The Transmit Status And Control Register is shown in

Figure 13-1, while the Receive Status And Control

FIGURE 13-1: TXSTA REGISTER (ADDRESS: 15h, BANK 0)

R/W - 0

U - 0

R - 1

R/W - x

CSRC

TX9

TXEN

SYNC

—

TRMT

TX9D

R = Readable bit

W = Writable bit

-n = Value at POR reset

(x = unknown)

bit7

bit0

bit 7:

CSRC: Clock Source Select bit

Synchronous mode:

1 = Master Mode (Clock generated internally from BRG)

0 = Slave mode (Clock from external source)

Asynchronous mode:

Don’t care

bit 6:

TX9: 9-bit Transmit Enable bit

1 = Selects 9-bit transmission

0 = Selects 8-bit transmission

bit 5:

TXEN: Transmit Enable bit

1 = Transmit enabled

0 = Transmit disabled

SREN/CREN overrides TXEN in SYNC mode

bit 4:

SYNC: USART mode Select bit

(Synchronous/Asynchronous)

1 = Synchronous mode

0 = Asynchronous mode

bit 3-2:

Unimplemented: Read as '0'

bit 1:

TRMT: Transmit Shift Register (TSR) Empty bit

1 = TSR empty

0 = TSR full

bit 0:

TX9D: 9th bit of transmit data (can be used to calculated the parity in software)

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