Making Friends with the Production Team
Most engineers are aware of design for test and design for manufacture. The goal is to design products that are easy to test and manufacture. If you achieve this, you’ll have lots of friends in the production department.
I once heard that if you consider all the systems a typical car needs, you will need about four hours for programming and configuration. Although I’ve never been able to verify this, I was reminded of this figure when I recently came across another programming problem.
The problem was programming a data table during production. The look-up table (LUT) contains data to control an engine and maps all of the engine parameters under various operating conditions. The table was about 256Kbits. That’s no not unusually large so why the problem? The problem was that the LUT had to be measured and calculated during production. To compound the problem further, the table is arrived at iteratively and needs to be re-written many times.
Let’s just run through the calculations if you stored the LUT in an EEPROM:
| Programming time of EEPROM (assumes 32 byte write page and 10ms per page) |
10.24s |
| Cost of Programming 256Kbits (assume €30 per hour) |
8.5c |
| Cost of Programming 10 iterations of the LUT |
€0.85 |
| Time taken for 10 iterations of the LUT |
1min 44s |
Now I don’t know about you but I was surprised to calculate that the cost of programming a 32Kbyte 256Kbit) EEPROM is 8.5c. This of course assumes that you can only program one device at time.
Compare this to using an F-RAM. The programming time is basically the bus speed.
| Programming time of F-RAM (assumes 8MHz SPI clock – no write time required) |
0.262s |
| Cost of Programming 256Kbits (assume €30 per hour) |
0.22c |
| Cost of Programming 10 iterations of the LUT |
€2.2c |
| Time taken for 10 iterations of the LUT |
2.62s |
Now if you go the production department and tell them that you could save them 1min 41s of production time and will save €0.82 (at €30 per hour) you will make lots of people happy!
F-RAM Design Hints | Duncan Bennett | 
March 12, 2010 9:50 am
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