CD1865 datasheet(76/150 Pages) INTEL

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CD1865 — Intelligent Eight-Channel Communications Controller

Datasheet

7.3.5

Transmitter Hardware (Out-of-Band) Flow Control

Transmit Out-of-Band Flow Control is performed automatically by the CD1865 by the CTS* pin,

if the CTS Auto Enable (CtsAE) mode is enabled in bit 1 of COR2. In this mode, before a character

from the FIFO is transmitted, the CTS* pin is tested, and, if inactive, transmission is delayed. Since

flow control is implemented between the FIFO and the Transmit Holding register, when CTS* is

negated, it is possible to get both the current character being sent and the character in the Transmit

Holding register.

However, the Send Special Character Command (that is, Xon and Xoff) overrides CTS* inactive.

This is generally preferred; however, in some applications sample CTS* or CD* before sending a

special character.

To complete the handshake with a remote device, an RTS Automatic Output (RtsAO, bit 2) mode is

also provided. This causes the RTS pin to be asserted throughout any data transmission: normal,

break, and special characters. The RTS pin is activated whenever there is data in the FIFO and

transmitter registers. It is held active until after the last Stop bit of the last character is transmitted.

7.3.6

Transmitter Software (In-Band) Flow Control

The CD1865 transmitter can be programmed to respond automatically to flow-control characters

received by the receiver. This feature requires no host assistance and substantially reduces host

processing requirements. If this Automatic mode is enabled, when the remote unit transmits an

Xoff character to the CD1865 (to prompt the CD1865 to suspend transmission), the CD1865

terminates the transmission. The CD1865 may require approximately 500 microseconds (~2

character-times at 38.4 kbps) after receipt of the Stop bit to recognize that the character it has

Figure 26. Transmitter Flow-Control Logic

FULL/

EMPTY

BIT

TRANSMITTER HOLDING REGISTER

TRANMSITTER SHIFT REGISTER

TRANSMITTER

FIFO

BACKGROUND CODE:

FIFO-TO-H.R. TRANSFER, FLOW

CONTROL, OTHER FEATURES

FOREGROUND CODE:

BIT DISASSEMBLY,

H.R.-TO-S.R. TRANSFER

(POLLING LOOP)

(INTERRUPT-DRIVEN)

RTS

OUT

CTS

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