ToolLink User Manual
MKS Instruments, Inc.
Page 25 of 30
No Delimiters:
If the Start Delimiter String and Stop Delimiter String are both set to zero, the CDN466 will operate in a
“free running” mode. For Polled I/O messaging, all RX buffer bytes are returned in response to a Poll
Request message. If there are more RX bytes than will fit, then the remaining bytes are sent in the next
poll/explicit transaction. For free-running mode with Change-of-State messaging, each received byte will
generate a Change-of-State input message. Note that this is not an efficient use of DeviceNet bandwidth.
Start Delimiter String – Attribute 9
The Start Delimiter String is a constant sequence of characters the CDN466 uses to identify that beginning of
a received serial message when the Receive Mode attribute is in the “Start/Stop Delimiter” mode. The
number of bytes in the string can be 0 (not used) to 4. The Start Delimiter set as a DeviceNet
SHORT_STRING, which includes a length byte followed by the ASCII bytes defining the string. For example,
to use the four byte string “<<<<” is the SHORT STRING
“ 4, ‘<’, ‘<’, ‘<’, ‘<’ ” or “0x04, 0x3C, 0x3C, 0x3C, 0x3C”.
Stop Delimiter String – Attribute 10
The Stop Delimiter String is a constant sequence of characters the CDN466 uses to identify that beginning of
a received serial message when the Receive Mode attribute is in the “Start/Stop Delimiter” mode. The
number of bytes in the string can be 0 (not used) to 4. The Stop Delimiter set as a DeviceNet
SHORT_STRING, which includes a length byte followed by the ASCII bytes defining the string. For example,
to use the four byte string “>>>>” is the SHORT STRING
“ 4, ‘>’, ‘>’, ‘>’, ‘>’ ” or “0x04, 0x3C, 0x3C, 0x3C, 0x3C”.
Rx Handshake Enable – Attribute 11
By default (Rx Handshaking disabled), the CDN466 updates the data received from the serial connection
to the DeviceNet I/O response as soon as a complete message is received. At slow DeviceNet rates,
however, there remains the possibility that more than one serial message will be received between
successive polls, resulting in loss of data.
If the Rx Handshaking Enable is set, the serial data made available in the I/O response will not be
overwritten by a new message until the user acknowledges that the data has been received. Once the
user has acknowledged the new serial data by setting the Rx Acknowledge value equal to the Rx
Counter, the I/O response will be free to update with new data.
Important:
As the serial buffer may continue to receive data as the CDN466 is waiting for an
acknowledgement, the receive buffer may reach an overflow condition if new data is not acknowledged at
a sufficient enough rate.
Figure 1: Rx Handshaking
I/O Commad
Command
RX
ACKNOWLEDGE
TX Counter
Length
Data
Rx Handshaking Disabled:
No function. User sets to zero.
Rx Handshaking Enabled:
User sets to value of Rx Counter to acknowledge new data
