Problems reading a static RAM using MAX7300 modules on BS2P
southernbob
Posts: 34
The project:
Use 2 MAX7300 modules and a DS1248 (128K x 8 static ram w/battery backup) to form a data retention
unit. The first 7300 drives the address lines A0 - A16. The second 7300 drives the data lines and the
control signals (CE, WE, OE, negative active). Once figuring out how the MAX7300 modules work I
wrote a program for the BS2P using· I2C write (I2COUT and I2C read (I2CIN). It is a simple program
just writing an incrementing·pattern to an incrementing address (only using a small portion of the
static RAM). After writing a byte it·is read back and outputted to the DEBUG screen so I could
see if it was the correct data. It was. I changed the program to do a compare with the write data and
only go to the DEBUG screen on a non-compare. It ran error-free for as long as I would let it run.
The problem:
I commented out the write portion of the program and only did the read and I get garbage. I get 2
repeating characters, such as $FF $FE and then as the program runs for awhile it changes to
2 other repeating characters and continues changing back and forth between the 2 sets of
characters. When I look at the data lines from the RAM with a scope it appears that is what is
coming from the RAM, garbage. I changed the program back to do a write and just used fixed
data such as $55 and wrote the RAM. Going back to just a read I get the $55 data on the
DEBUG screen and the scope shows $55 coming from the RAM. I tried several other fixed
data and they all appeared to work. So, everything 'appears' to work except for the incrementing
pattern, but only when doing the read without the write . Anybody have any ideas,suggestions of
what could be wrong or things to try.? I have been working on this on and off for several weeks
now and just about to give up on it for the last time and put it in the 'FAILED' project list.
Bob
Use 2 MAX7300 modules and a DS1248 (128K x 8 static ram w/battery backup) to form a data retention
unit. The first 7300 drives the address lines A0 - A16. The second 7300 drives the data lines and the
control signals (CE, WE, OE, negative active). Once figuring out how the MAX7300 modules work I
wrote a program for the BS2P using· I2C write (I2COUT and I2C read (I2CIN). It is a simple program
just writing an incrementing·pattern to an incrementing address (only using a small portion of the
static RAM). After writing a byte it·is read back and outputted to the DEBUG screen so I could
see if it was the correct data. It was. I changed the program to do a compare with the write data and
only go to the DEBUG screen on a non-compare. It ran error-free for as long as I would let it run.
The problem:
I commented out the write portion of the program and only did the read and I get garbage. I get 2
repeating characters, such as $FF $FE and then as the program runs for awhile it changes to
2 other repeating characters and continues changing back and forth between the 2 sets of
characters. When I look at the data lines from the RAM with a scope it appears that is what is
coming from the RAM, garbage. I changed the program back to do a write and just used fixed
data such as $55 and wrote the RAM. Going back to just a read I get the $55 data on the
DEBUG screen and the scope shows $55 coming from the RAM. I tried several other fixed
data and they all appeared to work. So, everything 'appears' to work except for the incrementing
pattern, but only when doing the read without the write . Anybody have any ideas,suggestions of
what could be wrong or things to try.? I have been working on this on and off for several weeks
now and just about to give up on it for the last time and put it in the 'FAILED' project list.
Bob
