RS232 to J1962 Comms ideas/queries.

[xxalexx at ix.netcom.com]

> From:          martin at mgass.demon.co.uk
> To:            diy_efi at efi332.eng.ohio-state.edu
> Date:          Sun, 22 Mar 1998 14:30:19 +0000
> Subject:       RS232 to J1962 Comms ideas/queries.
> Priority:      normal
> Reply-to:      diy_efi at efi332.eng.ohio-state.edu

> This might be a bit off-subject for diy_efi,  but as it relates 
> to J1962 I'll post it anyway.....
> 
> ISO9141 describes intialisation on J1962 as follows :
> one start bit - logic 0,
> 8 address bits (LSB first to MSB last)
> one stop bit - logic 1.
> all at 5bps
> With an opto isolated i/f between car and PC, in RS232 terms
> I would think the easiest way to achive this is by holding DTR up and 
> down for the required number of milliseconds and making sure this 
> converts via the opto interface to the K line.....any comments ?
> 
> The key word format(from ECU) is one start bit (0), seven bits of key word 1, 
> parity, stop bit (1), then a time delay, then next word etc.
> In RS232 does the MSB or LSB of the byte go first ?
> I saw some references in the archive to 9141 being inverted relative 
> to rs232 ?   
> Assuming a baud rate of 10.4K (which is near enough achievable by adjusting the 
> divisor [by 11] when the mscomm setting (in VB) is 9600,8,n,1) what is the 
> nearest mscomm setting to the above key word format, which is 1 start, 7 data, 1 stop 
> with parity....or do i have to frig it as in the initialisation by 
> very carefull timings using (i.e. send each bit pulse out seperate as 
> opposed to using the RS232 TXD line) , say DTR.
> 
> Anybody able to offer any advice.
> 
> regards,
> 
> martin
> ----------------------------------------------------------
> martin at mgass.demon.co.uk
> ----------------------------------------------------------
> 
> 
I have system that works, I hope to offer it as share ware since
I have no money.  The interface fits in DB9 and converts 5
and 10400 baud with no optos.  How does CarComp do it ?
Do you have the optologic part number.
Presently working on 8142 baud Chrysler since I have a RAM van
available for a while.
alex