CD1865 Datasheet, PDF (78/150 Pages) Intel Corporation – Intelligent Eight-Channel Communications Controller

CD1865 — Intelligent Eight-Channel Communications Controller
The remote device can signal the CD1865 to resume transmission in one of two ways depending on
the setting of the Implied Xon mode (IXM) option bit COR2. When the IXM bit is set, the CD1865
resumes transmission upon receipt of any character, for example, each character is an implied Xon.
In Implied Xon mode it is assumed that if the remote is capable of transmitting data, it is able to
receive as well. If a character is treated as an implied Xon, no special status is recorded in the
RCSR, and the TxFlon bit is not set in the CCSR. An implied Xon character is not stripped if flow-
control transparency is enabled.
When the IXM bit is not set, the CD1865 only resumes transmission upon receipt of an Xon
character. In addition, the host may force a resumption of transmission by issuing a Transmit
Enable Command, which clears the TxFloff bit. The Xon and Xoff characters or character
sequences are equal in a Toggle mode. There is no special bit to enable this mode. The CD1865
detects this mode whenever the Xon character equals the Xoff character, and it implements Toggle
mode automatically.
In Toggle mode, whenever the special character is received, the current state of flow control is
toggled. If flow control transparency is set, the character is dropped. If not in flow-control
transparency, the character is passed to the host. If it is a single character, the special character
status is ‘1’ and the character is put in the Receive Data FIFO. In two-character sequence, the
second character is placed in the Receive Data FIFO along with special character ‘1’ in the Status
FIFO.
The TxFloff and TxFlon bits indicate channel status when the remote device is flow-controlling the
CD1865 transmitter. When the remote requests the CD1865 to stop transmission, the CD1865 sets
the TxFloff Status bit in the CCSR. If TxFloff is set, the last flow-control character received was a
flow-off. When the remote sends an explicit flow-on character, the CD1865 clears the TxFloff bit,
and set the TxFlon bit. (If flow is resumed because of implied Xon, TxFloff is cleared, but TxFlon
is not set). When the CD1865 resumes transmission, the TxFlon bit is cleared. Transmit Flow
Status bits is also cleared by enabling or disabling the transmitter or resetting the channel.
This is summarized in the table below:
TxFloff
1
1
0
0
TxFlon
1
0
1
0
Meaning
Illegal
Transmitter is flow-controlled off
Transmitter on, no data sent yet
Transmitter on, CD1865 has sent data, or implied Xon has
occurred. This is also the ‘normal’ state of these bits when flow
control is not being used
7.4
Modem Signals and General-Purpose I/O
Each channel of the CD1865 has four pins that can be used either as modem-control or general-
purpose input/output pins. The modem signal names assigned to these four pins have been chosen
to provide an easy reference for systems designers. In fact, they are all simply general purpose
inputs and outputs (if automatic Out-of-Band Flow Control is not used) that can be individually
controlled by the modem signal value register(s). Since they are general purpose, system designers
may choose to connect the pins in any way that suits the application.
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Datasheet