请高手指教modbus

我用VB编程读写s7-200.现在读数据可以,但写不了.请高手帮忙看看.
Private Sub Command4_Click()
Dim send(11) As Byte
Dim bh1 As Byte
Dim bh2 As Byte
send(0) = 1
send(1) = &H10
send(2) = 0
send(3) = 0
send(4) = 0
send(5) = 1
send(6) = 2

send(7) = &H11
send(8) = &H22

Call crc(send, 9, bh1, bh2)
send(9) = bh2
send(10) = bh1
MSComm1.Output = send
End Sub
S7-200返回01 90 02 CD C1
crc校验没有问题,读数据没有问题.

crc没有错,我读数据和置位I0.0都没有问题啊.写的时候s7-200也返回数据了.不过是错误的数据01 90 02 CD C1

这是我的读数据的,这个没有问题.
Private Sub Command2_Click()
Dim send(8) As Byte
Dim bh1 As Byte
Dim bh2 As Byte
send(0) = 1
send(1) = 3
send(2) = 0
send(3) = 0
send(4) = &H0
send(5) = 10
Call crc(send, 6, bh1, bh2)
send(6) = bh2
send(7) = bh1
MSComm1.Output = send
End Sub