CD1865 datasheet(65/150 Pages) INTEL

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Intelligent Eight-Channel Communications Controller — CD1865

Datasheet

Bits affecting flow control are summarized below.

The FCT bit controls whether flow-control characters are passed on to the host. It has meaning only

when In-Band flow control is enabled, that is, TxIBE is set. When the CD1865 receives a flow-

control character or character sequence and FCT is a ‘0’, it starts or stops the transmitter, as

required, and passes the character onto the host as a Receive Exception. Since there is a one-to-one

correspondence between the Status and Receive FIFO, the flow-control character detected is stored

in the Receive FIFO, and a status byte indicating special-character detect is stored in the Status

FIFO. If FCT is a ‘0’, RxSC must be set to enable service requests to be issued to the host.

Otherwise, flow-control characters cannot be passed as Receive Exceptions and is instead passed

as Good Data.

If the FCT bit is a ‘1’, the CD1865 still starts or stops the transmitter, as required, but the

character(s) are discarded, and no exception is posted. In either case, the flow-control status of the

transmitter (on or off) is maintained by the CD1865 in the Channel Control Status register (CCSR).

The FCT bit makes it possible to support ‘escaping’ of flow-control characters. Some systems

follow a convention where two identical flow-control characters in a row indicates that flow

control is not to be performed, but rather one flow-control character is to be kept in the normal

received-data stream, and the other ‘escape’ character is to be discarded. If the CD1865 is in such a

system, set the FCT bit to a ‘0’, allowing flow-control characters to pass onto the host. When the

host detects two flow-control characters in a row, it simply restores the proper flow-control state of

the channel and discards one of the characters. However, for most systems the FCT bit can be set to

a ‘1’, reducing loading on the host.

7.1.9.1

No New Data Received Time-Out

It is sometimes useful for the host to sense that ‘no data has arrived lately’, when managing

relatively large I/O buffers. This event is used to flush the buffer up to the host for processing. One

of the receive timer options, No New Data Time-out (NNDT), generates a service request for the

first Receive Data Time-out following the transfer of all data from the channel to the host. This

service request is a Receive Exception sub-type, and can be enabled or disabled by controlling the

NNDT bit in the . Refer to Figure 23 on page 67 for the timer logic.

The timer is started only on data arrival. If the CD1865 processor determines that the Receive FIFO

is empty, the timer has expired, and there is a previous receipt of Good Data (and the timer feature

is enabled), a Receive Exception occurs with a status indicating that a time-out has occurred.

If the last Receive Exception Service Request was triggered by a time-out (to avoid ‘stale’ data) the

No New Data Time-out Service Request occurs immediately after the Data Transfer Service

Request completes. If the last service request was triggered by reaching the threshold, the timer

Bit Name

Function

SCDE

COR3

Enables Special Character Recognition.

TxIBE

COR2

Enables Automatic Transmitter Flow-Control.

FCT

COR3

Sets Transparency mode of flow-control.

XonCH

XoffCH

Xon

Xoff

SCHR1

SCHR2

SCHR1

(SCHR2 and SCHR4)

(SCHR1 and SCHR3)

SCHR2

(SCHR1 and SCHR3)

(SCHR3 and SCHR4)

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