CD1865 Datasheet, PDF (19/150 Pages) Intel Corporation – Intelligent Eight-Channel Communications Controller

Intelligent Eight-Channel Communications Controller — CD1865
Service requests to the host system are implemented on the CD1865 by three hardware service
request state machines. Each machine has the ability to ‘queue-up’ multiple requests. The state
machines are designed to offer the fastest response possible. Whenever the CD1865 processor
determines that a condition needs a service request, it queues the request with the appropriate state
machine. The state machine posts the external request, monitors acknowledgment cycles from the
host, and informs the CD1865 processor when a valid service acknowledgment has been
completely serviced. This allows the CD1865 to correctly maintain the internal context for
processing the channel being serviced.
Because the CD1865 processor processes every character sent or received, features such as
Automatic Flow Control and Special Character Recognition are easily implemented. This reduces
the processing burden on the host system. Both In-Band (Xon, Xoff) and Out-of-Band (RTS/CTS,
DTR/DSR) Flow Control modes are supported. For In-Band Flow Control, the CD1865
automatically starts and stops its transmitter when the remote unit sends flow-control characters.
The CD1865 makes it easy for the local host to flow-control the remote by the ‘Send Special
Character’ commands. For Out-of-Band Flow Control, the transmitter optionally asserts RTS and
monitors CTS for permission to send, and assert/negate DTR when the Receive FIFO reaches a
user-definable threshold. DSR can be used to gate the receiver on and off. Together, the In-Band
and Out-of-Band features allow the data flow to be controlled in realtime with minimum or no host
intervention, and this also prevents loss of data.
Systems with multiple CD1865s are easily implemented, with no external glue, by a daisy-chain
scheme. A fair-share feature ensures equal access for all service requests, both within one CD1865
and across multiple devices. Alternately, multiple CD1865s can be operated in parallel as
independent devices.
Serial channels on the CD1865 are entirely independent of one another. Any channel can be
programmed to a combination of features regardless of the state of other channels. Bit-rate
generators are programmed by loading a divisor value, so the transmitters and receivers can each
operate at any standard or non-standard data rate.
The CD1865 can detect the received line-break condition, send break characters of any length, and
transmit delays. This is done by transmit commands embedded in the Transmit Data Stream. The
CD1865 can also be programmed to detect user-defined special characters and generate a special
service request to the host. Parity checking is performed automatically, but can be overridden by
the host to force parity errors for test purposes. Character length and Stop bit length are also
programmable per-channel.
Modem pins on the CD1865 are general-purpose, that is, they are not hard-wired into the UART
functions. If modem pins are not needed to interface to actual modems, they can be used as
general-purpose I/O pins. In either case they are readable and writable directly by the host system.
In addition, the CD1865 can be programmed to monitor levels on modem input pins and generate
service requests to the host upon detecting a specified change.
The CD1865 is fabricated in an advanced CMOS process. Its high throughput, low-power
consumption, and high level of integration permits system designs with minimum parts count,
maximum performance, and greater reliability.
There is a significant difference between the CD1865 and conventional dumb UARTs; the CD1865
is more efficient and intelligent, even when operating in a polled environment. Systems built with
the CD1865 interface between the host and the I/O device at a higher level than systems built with
conventional UARTs. For example, with a dumb UART, the host must test each channel for
presence of data, a process that is time-consuming. With the CD1865, the host queries the entire
Datasheet
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