Yaskawa SMC–4000 - Manual (Page 47)

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SMC–4000 User Manual
additional message could look like a bad message to the SMC, causing another '?<cr><lf>'. Note that
it is not neccessary to flush th ebuffer during normal communication.
8) Do not use `VAR=<cr>' to request the SMC to return a variable value. If there was an error in
transmission, and the string that the SMC received was not a variable that already exists in the
controller, it creates a new variable. If this happens enough times, the controller will fill its variable
space. We recommend using `MG VAR<cr>' which is more reliable, meaning if a bad transmission
occurs, the SMC will respond with a '?<cr><lf>', and not create an unwanted variable. Note: Use the
'LV<cr>' (List Variables) command to see if there are any erroneous variables in the controller.
9) Use the 'TC<cr>' command to get the error code if a question mark ever appears in a response string.
Ethernet Configuration
Communication Protocols
The Ethernet is a local area network through which information is transferred in units known as packets.
Communication protocols are necessary to dictate how these packets are sent and received. The
SMC–4000 supports two industry standard protocols, TCP/IP and UDP/IP. The controller will
automatically respond in the format in which it is contacted.
TCP/IP is a "connection" protocol. The master must be connected to the slave in order to begin
communicating. Each packet sent is acknowledged when received. If no acknowledgement is received,
the information is assumed lost and is resent.
Unlike TCP/IP, UDP/IP does not require a connection. This protocol is similar to communicating via
RS232. If information is lost, the controller does not return a colon or question mark. Because the
protocol does not provide for lost information, the sender must re-send the packet.
Although UDP/IP is more efficient and simple, Yaskawa recommends using the TCP/IP protocol. TCP/IP
insures that if a packet is lost or destroyed while in transit, it will be resent.
Ethernet communication transfers information in ‘packets’. The packets must be limited to 470 data bytes
or less. Larger packets could cause the controller to lose communication.
*Note To avoid losing information in transit, Yaskawa recommends that the user wait for an
acknowledgement of receipt of a packet before sending the next packet.
*Note A command sent over an Ethernet Telnet session must reside in one packet. This means
that a Telnet emulator must not send a command such as MG_TPX<CR> until the
carriage return is present; i.e., do not send one character at a time as the user enters them.
Addressing
There are three levels of addresses defining Ethernet devices. The first is the Ethernet or hardware
address- a unique and permanent 6 byte number, or MAC address. Every device manufactured worldwide
has a unique Ethernet address. The SMC–4000 Ethernet address is set by the factory and the last two
bytes of the address are the serial number of the controller.
The second level of addressing is the IP address. This is a 32-bit (or 4 byte) number. The IP address is
constrained by each local network and must be assigned locally. Assigning an IP address to the controller
can be done in a number of ways.