一个与变频器通讯的小程序，I0.3和I0.4给的是频率，点一次就可发送过去，而I0.0（正转）I0.1（反转）I0.2（停止）却要点两次才能发送过去，这是为什么？下面贴上程序(使用西门子modbus库文件)
LD SM0.0
= L60.0
LD SM0.0
= L63.7
LD L60.0
CALL SBR1, L63.7, 9600, 0, +1000, M20.2, VB502

LD SM0.0
= L60.0
LD I0.3
O I0.4
EU
= L63.7
LD L60.0
CALL MBUS_MSG:SBR2, L63.7, 1, 1, 40003, +1, &VB606, M20.1, VB506

LD SM0.0
= L60.0
LD I0.0
O I0.1
O I0.2
EU
= L63.7
LD L60.0
CALL MBUS_MSG:SBR2, L63.7, 1, 1, 40002, +1, &VB600, M20.2, VB508

LD I0.0
O M0.1
AN I0.1
AN I0.2
= M0.1

LD M0.1
MOVW 16#1, VW600

LD I0.1
O M0.2
AN I0.0
AN I0.2
= M0.2

LD M0.2
MOVW 16#02, VW600

LD I0.2
O M0.5
AN I0.0
AN I0.1
= M0.5

LD M0.5
MOVW 0, VW600

LD I0.3
O M0.3
AN I0.4
= M0.3

LD M0.3
MOVW 2500, VW606

LD I0.4
O M0.4
AN I0.3
= M0.4

LD M0.4
MOVW 5000, VW606