TIR2000 datasheet(26/63 Pages) TI

26 / 63 page

2–14

2.1.6.1

Auto-flow Control (See Figure 2–4)

Auto-flow control is composed of auto-CTS and auto-RTS. With auto-CTS, CTS must be low before the

transmit FIFO register can emit data (see Figure 2–4). With auto-RTS, RTS becomes high when the receiver

is empty or the threshold has not been reached. When RTS is connected to the CTS, data transmission does

not occur unless the receiver FIFO register has empty space. Overrun errors are eliminated when UART1

and UART2 are TIR2000 or other autoflow control devices with enabled flow control. When UART1 and

UART2 are not autoflow control devices with enabled flow control an overrun error occurs if the transmit data

exceeds the data receive FIFO-read capacity.

RCV

FIFO

Serial to

Parallel

Flow

Control

XMT

FIFO

Parallel to

Serial

Flow

Control

SIN

RTS

SOU

CTS

D7 – D0

XMT

FIFO

Serial to

Parallel

Flow

Control

RCV

FIFO

Parallel to

Serial

Flow

Control

SOUT

CTS

SIN

RTS

D7 – D0

UART1

UART2

Figure 2–4. Example of Auto-flow Contol (Auto-RTS and Auto-CTS)

2.1.6.2

Auto-RTS (See Figure 2–4)

Auto-RTS data-flow control originates in the receiver timing and control block and is linked to the

programmed RCV-FIFO trigger level. When the receiver FIFO trigger level reaches a trigger level of 1, 4,

8, or 14 in the 16-byte mode or 1, 16, 32, or 56 in the 64-byte mode, RTS is de-asserted. The sending UART

may send an additional byte after the trigger level is reached (assuming the sending device has another byte

to send) because it may not recognize the de-assertion of RTS until after it begins to send the additional

byte. RTS is automatically reasserted when the RX FIFO register is emptied by reading the receiver-buffer

2.1.6.3

Auto-CTS (See Figure 2–4)

The transmitter circuitry checks CTS before sending the next data byte. If CTS is low, the transmitter sends

the next byte. To stop the transmitter from sending the following byte, CTS must be released before the

middle of the last stop bit that is currently being sent. The auto-CTS function reduces interrupts to the host

system. When the flow control is enabled, the CTS level changes and does not trigger host interrupts

because the device automatically controls its own transmitter. Without auto-CTS, the transmitter sends any

data present in the transmit FIFO register and a receiver overrun error can result.

To enable the auto-RTS and auto-CTS modes of operation bit 5 of the modem-control register must be set

to a 1.

TIR2000 데이터시트(PDF) 26 Page - Texas Instruments

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