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STX 02H 報(bào)文開(kāi)始
ETX 03H 報(bào)文結(jié)束
幀格式
STX CMD DATA ...... DATA ETX SUM(upper) SUM(lower)
例子
STX ,CMD ,ADDRESS, BYTES, ETX, SUM
02H, 30H, 31H,30H,46H,36H, 30H,34H, 03H, 37H,34H
SUM=CMD+......+ETX
30h+31h+30h+46h+36h+30h+34h+03h=74h;
累加和過(guò)兩位取低兩位


1 DEVICE READ 讀出軟設(shè)備狀態(tài)值
計(jì)算機(jī)向PLC 發(fā)送
始 命令 首地址 位數(shù) 終 和校驗(yàn)
STX CMD GROUP ADDRESS BYTES ETX SUM
例子從D123 開(kāi)始讀取4 個(gè)字節(jié)數(shù)據(jù)
02h 30h 31h,30h,46h,36h 30h,34h 03h 37h,34h