Hi
The dual function of pin 4 is not confusing if you know about it but there
is
still a lot of literature about which is based on RS232c where the CA
function
was the only possibility. The name RTS is imho better suited to CA.
<Quote>
EIA-232-D Interface Connector Pin Assignments
---------------------------------------------
Pin Number Function Circuit (Source) Signal Type
----------------------------------------------------------------------------
--
1 Shield -- --
2 Transmitted Data BA (DTE) Data
3 Received Data BB (DCE) Data
4 Request to Send CA/CJ (DTE) Control
(1)
<snip>
(1) When hardware flow control is required, Circuit CA may take on the
functionality of Circuit CJ.
<snip>
Request to Send (Circuit CA)--conditions the local DCE for data
transmission, and controls the direction of transmission on half-duplex
channels. On half-duplex channels, Circuit CA maintains the DCE in the
transmit mode and inhibits the receive mode; on simplex channels, it
maintains the DCE in the transmit mode. An OFF to ON transition on Circuit
CA causes the DCE to enter transmit mode and turn Clear to Send ON. An ON
to OFF transition causes the DCE to complete the data transmission, enter
the receive or nontransmit mode, and turn Clear to Send OFF.
<snip>
Ready for Receiving (Circuit CJ)--controls data transfer (flow control) on
Circuit BB (Received Data) when an intermediate function such as error
control is being used in the DCE. The ON condition indicates that the DTE
is capable of receiving data, while the OFF condition indicates that the
DTE is not capable of receiving data and causes the DCE to retain the data.
In some DCEs, the OFF condition also causes a signal to be transmitted to
the distant DTE causing an OFF condition to be placed on Circuit CB (Clear
to Send) extending the flow control to the distant DTE.
quoted from http://163.18.14.55/datapro/06795-1.htm
Jon.
-----Original Message-----
From: ZN [mailto:[EMAIL PROTECTED]]
Sent: 08 May 2001 15:25
To: [EMAIL PROTECTED]
Subject: RE: Re: [ql-users] QL serial ports
On 5/8/01 at 11:37 AM [EMAIL PROTECTED] wrote:
>> Simple - you need a crossover lead.
>> TX -> RX
>> RX <- TX
>> RTS -> CTS
>> CTS <- RTS
>
>> and that is it.
>> No complications with DSR and DTR - forget them.
>
Sometimes you need to tie DTR and DSR together inside the plug on both
sides.
I don't know what all the confusion is about - there are really 6 relevant
signals (and ground), 3 in either direction. Normally they need to be tied
like this: TX <-> RX, RTS <-> CTS, DTR <-> DSR. TX, RX are the serial data,
RTS/CTS are the handshake lines, which are data relevant and can change on
a serial byte per byte basis, and DTR/DSR are peripheral status signals,
which tell you that the port or in fact the device the port is on, is even
active.
The fact that some of these are mislabelled on the QL is not the problem of
RS232 - it might as well have been an error in the manual.
Of course, the 'change' in direction regarding DTE/DCE and male/female
connectors is the biggest RS232 snafu, the best way to get around that is
to use a tester or voltmeter!
On RS232D the apparent change in RTS function is just a change of name - if
you look at the function carefully, it's all the same thing.
Nasta
