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Hardware expansion
Non-volatile clocks
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The TDS9092 keeps date and time as standard, even in the low power 3mA mode. You can keep these even with the card switched off, in any of three ways:


q       SMARTWATCH: a socket which plugs into the TDS9092 application position, and the final PROM goes into this. The type number is Dallas Semiconductor DS1216E. You read and write the date and time by means of W@ and W! which you'll find in the TDS9092 library software routine _SMART.TDS. Usually you use W@ to set the board clock in the power-up initialisation and when you want the time read it from there (see TIMEKEEPING). Occasionally, for instance once a day, you may update the board clock by re-using W@ .
  To set the Smartwatch first adjust the board clock date and time with NOW and HOURS and then use W! to write it into the device.
  The clock is kept non-volatile by means of lithium batteries within the device. Turn off the TDS9092 and the time & date are still correct when you power up again. Note that the Smartwatch does not work with RAM, only PROM so:

1. get your program working in RAM
2. add W@ in the word entered at power-up
3. make the application PROM and test it
4. set date and time with something like

   21.00.00 HRS 25.12.94 NOW W!

The nice thing about this solution is that there is no hardware to make. Just plug in and go.

q       PCF8573P: This is a 16-lead dual-in-line clock device which can be connected to the TDS9092 by just the two-wire I2C bus and +5V power supply. It is made non-volatile by adding a back-up battery. A particular feature of this chip is an output which becomes valid when the clock matches a pre-set alarm time. This can used to switch on a TDS9092 at regular intervals, with only the clock chip current of 10ľA in between. The chip also provides square waves with 1 second and 1 minute periods. Software support is in file _PCF8573.TDS.

q       PCF8583FP: This is an 8-lead clock device available in surface mount and is the clock used on the TDS2020F, the TDS9092's more powerful cousin. It can be connected to the TDS9092 by just the two-wire I2C bus and +5V power supply. Features are similar to PCF8573P but it lacks second and minute outputs. Software support is in file _PCF8583.TDS .

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