CD1865 datasheet(79/150 Pages) INTEL

79 / 150 page

Intelligent Eight-Channel Communications Controller — CD1865

Datasheet

However, when the system software design chooses to make use of the automatic Out-of-Band

Flow Control with the pins, then the signal naming convention no longer holds true in some cases,

depending on whether the device is used as DCE or DTE. In this case, it is best to think of the pins

in terms of their actual uses within the CD1865 and connect them accordingly, without regard to

their names. The RTS* and CTS* pins are associated with the transmitter and the DTR* and DSR*

pins are associated with the receiver. The table below shows Intel’s recommended signal hook-up if

automatic, Out-of-Band Flow Control is required.

For example, if the CD1865 is designed to be a DCE and automatic Out-of-Band Flow Control is

required, the pin labeled DTR should be connected to remote CTS input. If the CD1865 is to be

used as the DTE side, then the CD1865 CTS output would be connected to the remote CTS input.

Note that if automatic Out-of-Band Flow Control is implemented, the activity of DTR and DSR

pins do not implement the function assigned to those signal names by the signalling conventions of

the CCITT and other standards organization. These names would only apply to these pins if they

are under program control and not under automatic CD1865 control. In fact, the ‘DTR’ function, as

defined, enables the modem to go on- and off-line, depending on the state of the pin. If automatic

control is used, then DTR would go inactive when the receive FIFO reached the programmed

threshold thus causing the modem to drop the connection (carrier) to the remote, which would not

be the correct function. Refer to Section 7.3 for details on operation of modem pins in flow-control

applications.

Modem pins are implemented as I/O ports accessible by either the CD1865 processor or the host.

The modem pins are not connected directly to the transmit or receive hardware. When a user

programs out-of-band modem functions to be active, the CD1865 processor reads from and writes

to these pins. Specifically, when RTS* and CTS* are being used for transmit flow control, the

CD1865 processor asserts RTS* and senses CTS*, as required. Likewise, when configured to do

so, the Receive FIFO negates DTR* when full. The host should not be allowed to re-assert it

inadvertently. The host is not ‘locked out’ of accessing these bits; care should be taken so that these

bits are not written to, causing the system to malfunction.

The user has direct control over the RTS* and DTR* Outputs and can sense the state of CTS*,

CD*, and DSR* Inputs through the Modem Signal Value register (MSVR). Since the host is

accessing these pins directly, there is no delay in the host's ability to detect a level change. DTR*

and CD* depend on the state of the DTRSEL input.

DCE

DTE

CD1865 Pins

Out-of-Band Flow Control

CTS

DTR

Signal remote to transmit

RTS

Not implemented in this direction

RTS

Request remote permission to transmit

CTS

Enable transmitter

Modem

Control Pins

Function

RTS*

Request to Send (general-purpose output)

CTS*

Clear to Send (general-purpose input)

DTR*

Data Terminal Ready (carrier detect/general-

purpose input/output)

DSR*

Data Set Ready (general-purpose input)

CD*

Carrier Detect (general-purpose input)

CD1865 Datasheet(PDF) 79 Page - Intel Corporation

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