I don't understand the point of "data flow requirement". Of course any handshake slows down any communication - that's why it is used at all!

Speaking technically, if DTE-DCE communication speed on one endpoint is lower than the other endpoint and that is lower than DCE-DCE, the DCE-DCE connection must have implemented some means of handshake - although this is usually hidden for the user; but the DTE on the "faster" endpoint MUST have implemented some handshaking (throttling the DTE->DCE path).

If DTE-DCE speed is higher than DCE-DCE, there MUST be some handshaking implemented on both DTE-DCE interface (for the DTE->DCE direction).

Handshaking is not required only if both DTE-DCE speeds are the same and are below the DCE-DCE speed; or if the length of data packets is below the minimum buffer of each device in the chain, and the average data speed is below the capability of the slowest interface. Generally, I would not count on any of these.

In the case of the enquirer, if the DCE is really capable of only 115200 baud (even if that is NOT the physical bandwidth, using compression at the DCE it IS possible that the data flow is such high locally!), and the mcu has an UART capable of 115200 baud, but the program is not able to process a data stream at that speed, implementing handshake solves him the problem.


Jan Waclawek

PS. Terminology:
DTE - Data Terminal Equipment = in this case PC or microcontroller
DCE - Data Communication Equipment = in this case mobile phone (modem)