HESG324442R111工控卡件
直到发出一次读取，只能有一次挂起的读取传输。通常在每个读取周期开始时发出读取。如果在读取期间未完成挂起的读取传输，则通道错误位和详细通道状态字将被设置为指示非致命周期错误。如果周期错误发生在第一次传输时，COMMREQ状态也将指示非致命周期错误。如果时间单位数为零，则上一次传输完成后，将立即发出后续传输。在这种情况下，不会出现周期错误。（字12）每次读取超时：字12指定以太网接口在设置通道错误位和详细通道状态字以指示非致命超时错误之前等待读取传输完成的时间（以百分之一秒为单位）。如果第一次传输发生超时错误，COMMREQ状态也将指示非致命超时错误。对于大多数应用程序，不需要超时，因为读取周期充当超时。（单词12应为零表示无超时）。但是，建议在两种情况下指定超时：▪ 当时间单位数（字11）为零时，以便在上一次传输完成后立即发出后续传输，并且不会报告周期错误。在这种情况下，可以指定超时值，以便通道错误位报告超时错误。▪ 当读取周期非常长（分钟或小时）时。在这种情况下，可以指定一个较短的超时值，这样应用程序就不必等待读取周期到期后再执行操作。（字13）本地PLC-存储器类型：字13–14指定本地PLC中以太网接口将存储从远程PLC接收的数据的位置。请参见下一节中的表格。要传输的数据量由从远程PLC读取的数据的存储单元的数量指定（字17）。有关更多信息，请参阅本节中的可用读取通道内存类型。（字14）本地PLC-存储器起始地址：字14确定本地PLC中存储远程PLC数据的起始地址。输入的值是从字13中指定的存储器类型和模式的PLC存储器开始的偏移量（从1开始）。根据指定的模式（例如，如果字13=16，字14=2，则起始地址将为%I9），此偏移量将以位、字节或字为单位。值的有效范围取决于PLC的内存范围。用户负责确保该区域足够大，可以包含请求的数据，而不会覆盖其他应用程序数据。（字15）远程PLC-存储器类型：字15–16指定要从中读取数据的远程PLC中的存储器类型和起始地址。有效值或%L）（零终止和填充）字28–31远程PLC-程序块（访问远程%L所需）（零结束和填充）内存位置16-31的进一步注意事项（字16）远程PLC-内存起始地址：字16确定远程PLC中读取数据的起始地址。输入的值是从字15中指定的存储器类型和模式的PLC存储器开始的偏移量（从1开始）。此偏移量将以位、字节或字为单位，具体取决于模式
up to issue a single read can have only one pending read transfer. A read will normally be issued at the start of each read period. If the pending read transfer has not completed during the read period, the Channel Error bit and Detailed Channel Status words will be set to indicate a non-fatal period error. If the period error occurs on the first transfer, the COMMREQ Status will also indicate a non-fatal period error. If the Number of Time Units is zero, a subsequent transfer will be issued as soon as the previous transfer completes. In this case, no period errors can occur. (Word 12) Timeout for Each Read: Word 12 specifies the time (in hundredths of a second) the Ethernet interface will wait for a read transfer to complete before setting the Channel Error bit and Detailed Channel Status words to indicate a non-fatal timeout error. If the timeout error occurs on the first transfer, the COMMREQ Status will also indicate a non-fatal timeout error. For most applications, a timeout is not needed because the read period acts as a timeout. (Word 12 should be zero for no timeout). However, there are two circumstances in which specifying a timeout is recommended: ▪ When the number of time units (Word 11) is zero, so that a subsequent transfer will be issued as soon as the previous transfer completes and no period errors are reported. In this case, a timeout value can be specified so that the Channel Error bit will report timeout errors. ▪ When the read period is very long (minutes or hours). In this case, a shorter timeout value can be specified so the application doesn’t have to wait for the read period to expire before acting. (Word 13) Local PLC - Memory Type: Words 13–14 specify the location in the local PLC where the Ethernet interface will store data received from the remote PLC. Please see the table in the following section. The amount of data to be transferred is specified by the number of memory units of the data read from the remote PLC (Word 17). For more information, refer to Read Channel Memory Types Available in this section. (Word 14) Local PLC - Memory Starting Address: Word 14 determines the starting address in the local PLC in which the data from the remote PLC is to be stored. The value entered is the offset (1-based) from the beginning of PLC memory for the memory type and mode specified in Word 13. This offset will be either in bits, bytes, or words depending on the mode specified (for example, if Word 13=16 and Word 14=2, then the starting address will be %I9). Valid ranges of values depend on the PLC’s memory ranges. The user is responsible for assuring that this area is large enough to contain the requested data without overwriting other application data. (Word 15) Remote PLC - Memory Type: Words 15–16 specify the memory type and starting address in the remote PLC from which the data is to be read. Valid values or %L) (zero-terminated and padded) Word 28–31 Remote PLC - Program Block (needed for access to remote %L) (zeroterminated and padded) Further Considerations for Memory Locations 16-31 (Word 16) Remote PLC - Memory Starting Address: Word 16 determines the starting address in the remote PLC from which the data is to be read. The value entered is the offset (1-based) from the beginning of PLC memory for the memory type and mode specified in Word 15. This offset will be either in bits, bytes, or words depending on the mode
