Master/Slave long-string examples?

Projects Networking, Protocols, and Devices
1

Hi, can anyone point me to any Master/Slave examples for requesting and returning strings of up to 200 characters please?

I've got an 'I/O' Nano which is monitoring port expander inputs and IR commands and must initiate appropriate responses to triggers, but there isn't enough remaining memory to also include reading of the responses from a config file on SDcard, so I want to off-load that task to a slave 'SD' Nano.
The 'I/O' master would send the triggering channel number to the 'SD' slave and request the corresponding channel number response line from the config file, then parse the returned string for sequences of voice files, IR transmit codes, relay combinations, and various other temperature, date and time alarms, durations and delay parameters etc.

The 'I/O' master is already using i2c for the port expanders and RTC, so I was planning to use the i2c for the 'SD' slave if I could (to make the most of memory) then hopefully at some future date might add an additional master 'Web Server' which could also request its page data from the SD slave. Anyway that was the plan, but I'm not an expert, and I can't figure out how to get past the Wire libraries 32 byte maximum i2c transfer limitation - so any alternative master/slave long string examples or suggestions would be appreciated.

2

You have to do more transmissions.

Having a Slave module that can be accessed by I2C is good. You can use that module in every project. However, when you buy an Ethernet Shield, there is a SD card socket also on that shield. Files or a webpage via I2C is slow, you don't want that.

I'm not happy with the Slave SD Arduino. The Master is waiting while the 200 bytes are being requested. The 200 byte with 32 per transmission needs 7 transmissions, and I2C is slow.

Must that config file really be a file ? Could you store it in (internal or external) EEPROM ?
Is it possible to add the SD to the Master and somehow make the code fit ?
Can you somehow think of another (hopefully better) solution ? Is the flash (code) or ram memory the problem ?

Could you use a single Arduino Mega 2560 board with Ethernet Shield ? that would be so much easier and you would be ready for the future.