參數(shù)資料
型號: CD1865
廠商: Intel Corp.
英文描述: Intelligent Eight-Channel Communications Controller
中文描述: 智能八通道通信控制器
文件頁數(shù): 41/150頁
文件大小: 871K
代理商: CD1865
Intelligent Eight-Channel Communications Controller
CD1865
Datasheet
41
There is a difference between the CD1865 and conventional dumb UARTs that makes the CD1865
more efficient even when operating in a polled environment. With a dumb UART, the host polls
each channel in turn to determine whether it has any data. With the CD1865, the host polls the
CD1865s as a group for whether it has data. If it does, the CD1865s indicates the channel, rather
than the host testing each channel in turn. In fact, it is not possible for the host to dictate which
channel is serviced; the CD1865 determines this order. This minimizes both the number of polling
steps required and the amount of time each needs. This also ensures fair, balanced service of all
channels.
There are several ways that a host system can poll the CD1865. Each method has certain
advantages. The most direct method is to read the Service Request Status register (SRSR). This
register contains three bits that indicate whether there is a request pending for receive, transmit, or
modem signal change, on the CD1865 being read. There are three more bits that provide the same
information for all CD1865s in the system
these three bits reflect the state of the wire-OR
ed
external request lines. Thus a single read operation can determine if there is any activity.
Figure 11. Simple Software Polled Interface Example
CD1865 #2
CD1865 #1
MICROPROCESSOR
A1
A3
A4
A7
D0
D7
A0
A2
A3
A6
A0
A2
A3
A6
D0
D7
D0
D7
RREQ*
TREQ*
MREQ*
RREQ*
TREQ*
MREQ*
ACKIN* ACKOUT*
ACKOUT* ACKIN*
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