说明书通讯描述：
A special procedure for transferring the character strings has been implemented between the software and an external PC. A start symbol
is sent, followed by the symbol of the string. An ends the string and a checksum of all strings in XOR format. For confirmation, the computers use (positive) and (negative). Using this procedure, transfer is much safer than using a pure ASCII-string without checksumtesting.
Using this record, a measurement value request can be realised by an external computer. The following have been implemented:
requesting measurement data bysending 'd' with the data record,
requesting the units of measurement with 'u' and
requesting alarms with 'a'.
国外工程师回复如下：
Send-String
string
The return should be if it is ok, otherwise
with
$02
$03
$06
$15
($ ist HEX)
defines as
{ xorsum=0, then for all string elements xorsum = (xorsum XOR (int)theString[i] ) }
that means, xor all stringelements as int values beginning with xorsum=0 and send is a byte value
大神帮帮忙吧，万分感谢rs232c是1969年eia制定的在数据终端设备dte和数据通讯设备（dce）之间的串行的二进制数据交换的接口，全称是eia-rs-232-c协议，也称eia-232，最初采用db-25作为连接器，包含双通道，但是现在也有采用db-9的单通道接口连接。其数字逻辑与电平之间的关系是：1：-3v~-25v，0：+3v~+25v。典型应用是微型计算机的串行接口。rs232ttl的本质是eia-rs-232-c协议的扩展，其采用三线通讯制，功能与rs232c的数据通讯线相同，而且一旦设备就绪，其接口是总是可以读写的，可以理解为rs232c中接口始终处于就绪状态（dtr，dsr，rts，cts始终接通）其数字逻辑与电平之间的关系是：0：0v~0.4v,1:+2.6v~5v(ttl标准)。其典型应用是mcs系列单片机和其它基于ttl规范的mcu。