View Full Version : How can I control 2 propeller chips w/1 EEPROM?

Dan E
11-13-2010, 12:41 AM
Hi, I'm doing a school project thats need close to 50 I/O's, and I have two 40 pin 32 I/O propeller chips. Is there a way to connect one to the other so that I can control all of the I/O's using just one EEPROM?

Clock Loop
11-13-2010, 12:59 AM
You can have the first prop boot from the eeprom, which then programs the second prop. You can also have the first prop do all the logic work for the second prop.

Follow my link and if you look at schematic, CUT off all 4884 props except the first one, that is then the master prop controlling slave prop circuit that uses a single eeprom.

This thread moves far into parallelism and so do attached circuits, program , but it also uses the concept of booting multiple props from a single eeprom & xtal.


The black box audio sequencer boots 4 props from a single eeprom & xtal using the master slave relationship.

Mike Green
11-13-2010, 01:26 AM
You can also use an I/O expander to provide additional I/O pins. A PCA9554 will provide 8 additional I/O pins and can be connected to the same pins used for the EEPROM. You can attach up to 8 of these since they have a 3-bit hardware address that's configurable.

If you need output-only, you could use 74HC595s to add 8 outputs each. These can be daisy chained so you'd only need 4 I/O pins for a series of them.

Dan E
11-13-2010, 05:44 AM
Thanks, both are very helpful solutions, I will give it a shot this weekend.

Dan E
11-21-2010, 02:03 AM
Hi, I was wondering if anyone knew how to write to pins on a slave chip from the master prop chip? Or if it is possible to have one program that can use pins on both chip?


Dan E

Mike Green
11-21-2010, 03:56 AM
You can't really do that. In other words, one Propeller can't "control" another Propeller or its I/O pins or anything else in that Propeller. Two Propellers can cooperate with one Propeller sending information to the second Propeller and a program in the second Propeller receives the information and interprets it in order to allow the first Propeller to appear like it's controlling the second one.

11-21-2010, 05:29 AM
In short, they cooperate.

Dan E
11-21-2010, 07:05 AM
Thanks for the help. I think I get it, so I can have the master prop access a program that is copiled into the slave prop, that program in the slave prop when adressed interrupts the main program in the master prop, and the program in the slave prop will be able to use its own I/O's?

11-21-2010, 07:25 AM
Yep. In short, you must coordinate.

11-25-2010, 09:16 PM
Hi, there are 2 methods, I would use the design pattern perfected by Clock Loop it works very well.

The other method which is sequential instead of parallel was designed by Godzich, Christian, Ken and Pems in 2008, it also works but has more limitations.


thank you
/Michael O'Brien