參數(shù)資料
型號: MC68HC05CJ4FB
廠商: MOTOROLA INC
元件分類: 微控制器/微處理器
英文描述: 8-BIT, MROM, 2.1 MHz, MICROCONTROLLER, PQFP44
封裝: QFP-44
文件頁數(shù): 61/114頁
文件大?。?/td> 361K
代理商: MC68HC05CJ4FB
GENERAL RELEASE SPECIFICATION
MC68HC(7)05CJ4
SERIAL COMMUNICATIONS INTERFACE
MOTOROLA
Rev. 2.1
8-13
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8.3.5 Idle Line Wakeup
To use this receiver wake up method in an actual system, a software device
addressing scheme is established to allow the transmitting device(s) to direct
messages to individual receivers or groups of receivers. This addressing scheme
is purely a software device and may take any form as long as all transmitting or
receiving devices are programmed to understand the same scheme. The
addressing information is usually the first frame(s) in a message so that
uninterested receivers are burdened with only these minimum addressing frames.
All receivers are awake (RWU bit is clear) when each message begins and as soon
as a receiver determines that the message is not intended for it, it sets its RWU bit
which inhibits flag setting until the RXD line goes idle at the end of the message.
As soon as an idle line is detected (in hardware) while the RWU bit is set, the
receiver hardware will force the RWU bit to zero so that the first frame in the next
message can be received. This method of receiver wake up requires that a
minimum of one frame time of idle line be imposed between messages and that no
idle time is allowed between frames within a message.
8.3.6 Address Mark Wakeup
In this method of receiver wake up, all serial frames consist of seven (or eight)
information bits plus an MSB which is used to indicate an address frame (when set
to one — “mark”). The first frame(s) of each message are addressing frames and
all receivers in the system evaluate these marked address frames to determine
whether or not the subsequent message is intended for a particular receiver. As
soon as a receiver determines that a message is not intended for it, it invokes the
receiver wake-up function (by setting RWU) so that no additional software
overhead is required for the rest of the message. When the next message begins,
its first frame will have the ninth bit set, which will automatically clear the RWU bit
and enable normal frame reception. The first frame whose ninth bit is set (address
marked) also will be the first frame to be received after wake up because RWU gets
cleared before the stop bit for that frame is serially received. This method allows
messages to include idle times, unlike the first wake-up method, but efficiency is
lost due to the extra bit time (address bit) which is required in all frames.
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