AXE027 UART flow control?

mhalbern

Member
Technical,

Does the AXE027 USB to serial cable employ any handshaking flow control?

My question comes from the fact that the AXE027 schematic diagram shows the FTDI FT232RQ chip with pins 8 and 32 tied together.

This connects RTS (request to send) to CTS (clear to send) and would suggest flow control handshaking.

However, I have constructed and tested this circuit and it works properly with RTS and CTS tied together or left unconnected, indicating that flow control is not implemented.

A little light on this matter is much appreciated.

Thank you in advance for a reply.
 

Goeytex

Senior Member
The ability to implement serial flow control would require that these signals/ pins be brought out the TTL serial side of the AXE027 adapter. They are not. With the AXE027 there is no access to RTS,CTS,DSR and DTR provided on the FT232RQ Chip.

Technical can explain why the RTS and CTS pins are tied together on the AXE027.
 

mhalbern

Member
Hi Goeytex,

Thank you for the reply.

Indeed, the fact that RTS, CTS, DSR, and DTR are not connected to the uC and yet RTS is connected to CTS in the AXE027 cable is one of this reasons for my posted questions.

I'm guessing that flow control is neither implemented or required.

Technical?
 

rossko57

Senior Member
yet RTS is connected to CTS in the AXE027 cable
It's a pretty standard practice; the Rev-ed software may well not use it, in which case it does no harm. But if it is implemented, then other folks software which does require it would work too.
 

Goeytex

Senior Member
For programming, the Programming Editor first sends a break. This tells the Picaxe that it is being programmed. The Picaxe then sends an ID that is confirmed by the Programming Editor. The programming editor then sends program data one byte at a time. The Picaxe being programed receives that byte and then repeats it back to be confirmed. If the bytes match then the programming editor sends the next byte .... and so on until done. There is no real flow control involved.
 

hippy

Senior Member
The FTDI chip supports hardware flow control but whether flow control is used or not depends upon how a COM port is opened by the application using it. None of the PICAXE programming software uses hardware flow control.

The CTS to RTS link within the AXE027 is, I would guess, to allow the cable to still be usable even if it is used with an application which opens the COM port with hardware flow control enabled.
 

Technical

Technical Support
Staff member
I'm guessing that flow control is neither implemented or required.
Connecting RTS to CTS inside the AXE027 at the time of the design was probably regarded as one extra way to be able to test if the correct type of cable was connected.

In practice it is not used, and no handshaking is required.
 

mhalbern

Member
Thank you Technical, et al. for your response to my inquiry.

Certainly this explains why the FTDI FT232RQ circuit operates equally well with the PICAXE regardless of the RTS to CTS connection.
 
Top