Originally Posted by gar  080201-0804 EST USA
True that drip feed (DNC) works with either XON/XOFF or RTS-CTS.
The major point of XMODEM is that it is an error detection and correction means that provides some advantage over simply using single parity bit checking on a character by character basis with no correction of any type.
Suppose you use single bit parity and the system receiving the character halts on a parity error. This has probably protected you from a potential crash, but the program stops.
Also suppose for whatever reason you lose a whole character and no parity error, and it was a decimal point. Now you may have a major crash. We have a customer with this kind of problem. XON/XOFF or RTS-CTS does nothing for you. These simply modulate the flow of data and nothing to do with noise induced errors.
XMODEM is a communication protocol that sends a fixed and known block of characters including a checksum. A data block is sent from a source to a destination and at the destination there must be a checksum match. If the match is good, then an OK acknowledgement is sent to the source and the source sends the next block, and so on. If the match is wrong, then a NOT OK message is sent to the source and the source resends the block. There is a count limit on the number of retries on the same block. When this is exceeded all communication is halted.
XMODEM will catch missing character errors as well as other random errors. Furthermore, XMODEM checks more of the system from some place within the source computer to some place within the destination. Usually the block of data goes into some buffer memory in the destination to have its checksum verified. The nearer this is to the final memory the better. A simple parity error check is usually only between the source and destination UARTs. Thus, more circuitry is checked with XMODEM than with a simple parity check.
The simple form of XMODEM used by HAAS does not have powerful error checking, but it is much better than the simple parity check between the UARTs.
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Yes. Xmodem is always better. If your older HAAS does not have Xmodem I do not think, any other external software will give you the same effect.