CD1865 datasheet(64/150 Pages) INTEL

64 / 150 page

CD1865 — Intelligent Eight-Channel Communications Controller

Datasheet

Because the CD1865 performs flow-control functions before the data is passed to the host, the

response time required of the host to avoid data overrun is greatly reduced. Additionally, the flow-

control characters can be stripped from the data stream, relieving the host from processing them.

To use automatic flow-control, the Special Character Detection (SCDE) must be enabled by bit 4 of

Channel Option register 3 (COR3). This causes all error-free received data to be compared for a

match with the Special Character registers (SCHR1–4). In addition, flow-control must be enabled

by Transmit In-Band Enable (TxIBE, bit 6) of COR2. This causes the special characters to be

interpreted as flow-control characters. For single-character flow-control sequences, SCHR1 is used

as Xon and SCHR2 as Xoff. SCHR3–4 are available for use as normal special-detect characters. If

two-character sequences are enabled by XoffCH and XonCH (bits 6 and 7) of COR3, SCHR1 and

SCHR3 form the Xon sequence, and SCHR2 and SCHR4 form the Xoff sequence.

If flow-control characters are passed to the host, they are marked as special characters 1 or 2 in the

Receive Channel Status register (RCSR). If a two-character sequence is detected, it is compressed

to the second character and a status indicating a match of the first character is set. A valid two-

character sequence requires that both characters be received without error; if an error occurs on the

second character the first character is treated as a normal character, and this does not affect non-

flow control special character detection.

CD1865 Datasheet(PDF) 64 Page - Intel Corporation