CD1284 Datasheet, PDF (59/176 Pages) Intel Corporation – IEEE 1284-Compatible Parallel Interface Controller with Two High-Speed Asynchronous Serial Ports

IEEE 1284-Compatible Parallel Interface Controller — CD1284
The CTS* input can also be monitored by the CD1284 and is a transmitter enable. The functions is
enabled by setting CtsAE (COR2[1]). If CtsAE is set, character transmission occurs only when the
CTS* input signal is asserted. If the signal is deasserted during active transmission, the current
character plus the character in the Transmitter Holding register are transmitted and transmission
ceases. Thus, a minimum of one and a maximum of two characters can be transmitted after the
control signal is deasserted. Transmission resumes when the signal(s) is reasserted.
The send special character command does not sample the CTS* or DSR* inputs. If the CPU opts to
send one of the special characters, the character is transmitted regardless of the state of these
inputs. This is preferable as the CPU can still flow control a remote even if it is being flow
controlled. If the state of CTS* and DSR* are important, they should be tested through
MSVR1[7:6] before the special character send command is issued.
5.6.4
Modem Signals and General-Purpose I/O
Each channel of the CD1284 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 provide an easy
reference for system designers. In fact, they are all simply general-purpose inputs and outputs (if
automatic out-of-band flow-control is not used) are individually controlled in the MSVRs. Since
they are general-purpose, system designers can opt to connect the pins any way to suit the
application.
DCE, DTE Application
When the system software design opts to use automatic out-of-band flow control, then the signal
naming convention no longer holds true in some cases, depending on if the device is used as DCE
or DTE. For this case, use these pins within the CD1284, connect them accordingly, and disregard
their names. The RTS* and CTS* pins are associated with the transmitter; the DTR* and DSR*
pins are associated with the receiver. Table 18 shows the Intel recommended signal hook-up for
automatic out-of-band flow control.
Table 18. Out-of-Band Pin Connections
DCE
CTS*
RTS*
–
–
DTE
–
–
RTS*
CTS*
CD1284 Pins
DTR*
–
RTS*
CTS*
Out-of-Band Flow
Control
Signal remote to
transmit
Not implemented in
this direction
Request remote
permission to transmit
Enable transmitter
For example, if the CD1284 is designed for DCE and automatic out-of-band flow control, connect
DTR* to the remote CTS* input. If the CD1284 is for the DTE side, then connect the CD1284
CTS* output to the remote CTS* input.
Note, if automatic out-of-band flow control is implemented, the activity of DTR* and DSR* do not
implement the function assigned to those signal names by the signaling conventions of the CCITT
(and other) standards organization. These pin names only apply to these pins if they are under
program control and not under automatic CD1284 control. In fact, the defined DTR function
enables the modem to go on- and off-line, depending on the state of the pin. If automatic flow
Datasheet
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