XR21B1411

8

ENHANCED 1-CH FULL-SPEED USB UART

REV. 1.2.0

1.3.5.1

Automatic RTS/CTS Hardware Flow Control

GPIO5 and GPIO4 of the UART channel can be enabled as the RTS# and CTS# signals for Auto RTS/CTS

flow control when GPIO_MODE[2:0] = ’001’. Automatic RTS flow control is used to prevent data overrun errors

in local RX FIFO by de-asserting the RTS signal to the remote UART. When there is room in the RX FIFO, the

RTS pin will be re-asserted. Automatic CTS flow control is used to prevent data overrun to the remote RX

FIFO. The CTS# input is monitored to suspend/restart the local transmitter (refer to Figure 5):

T r a n s m i tte r

A u to C T S

M oni t o r

R e c e iv e r FI FO

T r i gg er R eac hed

A u to R T S

T r i gge r Lev el

Re m o t e UA RT

UA R T B

RT S A #

CT S B #

TX B

RX A

ON

ON

OF F

ON

ON

OF F

1

2

3

4

1) C O M po r t ope ned , R X F I F O em p t y , R T S A # out put i s as s er t ed

2) S ignal pr opa gat ed t o C T S B # i np ut

3 ) D a ta b y te s e n te r T X F IF O , b e g i n tr a n s m i tti n g o n T X B

4) D a t a pr op agat es t o R e c ei v i ng dev ic e R X A

5) R X F I F O r ea c hes t hr e s hold

6) R T S A # d e - as s er t s

7) S ignal pr opa gat es t o C T S B # i np ut

8) T r ans m i s s i on s t op s on T X B

9) U S B B ul k - I n em pt i e s R X F I F O bel o w t hr es h ol d , R T S A # i s as s er t ed

10 ) S ignal pr opa gat ed t o C T S B # i np ut

11 ) D a t a by t es r e s um e t r an s m i t t i ng on T X B

5

6

7

8

9

10

11

RT S A #

C T S B #

TX B

RX A

C T SA#

TX A

R T SB#

RX B

R e c e iv e r FI FO

T r i gg er R eac hed

A u to R T S

T r i gge r Lev el

T r a n s m i tte r

A u to C T S

M oni t o r

L o c a l UA RT

UA R T A

1.3.5.2

Automatic DTR/DSR Hardware Flow Control

Auto DTR/DSR hardware flow control behaves the same as the Auto RTS/CTS hardware flow control

described above except that it uses the DTR# and DSR# signals. GPIO3 and GPIO2 become DTR# and

DSR#, respectively, when GPIO_MODE[2:0] = ’010’ and FLOW_CONTROL[2:0] = ’001’.

1.3.5.3

Automatic XON/XOFF Software Flow Control

When software flow control is enabled, the B1411 compares the receive data characters with the programmed

Xon or Xoff characters. If the received character matches the programmed Xoff character, the B1411 will halt

transmission as soon as the current character has completed transmission. Data transmission is resumed

when a received character matches the Xon character.

Software flow control is enabled when

FLOW_CONTROL[2:0] = ’010’.

1.3.6

Auto RS-485 Half-Duplex Control

The Auto RS-485 Half-Duplex Control feature changes the behavior of the GPIO5/RTS#/RS485 pin when

enabled by the GPIO_MODE register bits 2-0. See ”Section 3.1.1.13, GPIO_MODE Register Description

(Read / Write)” on page 18. The FLOW_CONTROL register must also be set appropriately for use in