[Coco] I2C - Is it possible?

[John Kent]

Sorry, wasn't thinking very clearly last night (it was the eraly hours 
of the morning here when I posted). You need both clock & data lines 
which means you need 4 signals, two transmit and two receive. That means 
you need RXD, TXD, RTS & CTS signals on the CoCo serial interface port, 
assuming they are bit bashed. You can use a MAX232 to do the RS232 level 
to TTL I2C conversion. You can find the datasheet online, and that 
should give circuit examples of how to wire it up.  The outputs to the 
I2C bus can be open collector with some pull ups. You can do that with a 
74HC(?)125 (?) by tying the input of each buffer section to the output 
enable pin. The transmit and open collector receive lines can be paired 
off and tied together.

Alternatively, you could use a PIC or AVR to make an RS232 to I2C 
bridge. I had an idea that NXP made some RS232 to I2C bridge chips.

John.

On 26/07/2011 5:05 AM, John Kent wrote:
>
> You need TXD, RXD and some handshake signal such as RTS to enable and 
> disable the TTL outputput from the receiver.
> You'd need something like a MAX242 except the EN* pin enables and 
> disables both the TTL RX inputs, one of which you want to be the 
> direction control. You'd wire the TTL RXD and TXD pins together.
>
> The only other way would be to use a MAX232 with a tri-state buffer on 
> the RXD output with the other handshake line controlling the output 
> enable.
>
> John.
>
>
> On 26/07/2011 4:13 AM, Nick Marentes wrote:
>> So, Is there a simple circuit to convert the RS-232 levels to IC2 
>> compatible levels (including the -5v)?
>>
>> If the RS-232 could be made 'electrically' IC2 compatible, then all 
>> that is left is the bit-banger software for the IC2 protocol right?
>>
>> Nick
>

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