==== DS3231 RTC ====
<wrap right>
{{:interfaces:zs-042-sch.jpg?200|ZS-042 schematic}}
</wrap>

There are at least two RTC modules containing the
DS3231 available from China. Both can operate with
the Raspberry Pi and one is designed especially
for it.

One useful feature of the DS3231 other than keeping
the time is its built-in temperature readout, however,
initial tests suggest that this is inaccurate.

=== DS3231 for Pi ===

This device is as simple as it gets. There are two pull-up
resistors for the I2C lines (4K3), a battery connected
to the VBAT pin and a capacitor on the power rails.

This device plugs directly into the GPIO header.

I bought two of these devices and one was faulty. Fixing it simply involved applying
pressure on each pin of the chip in turn with a hot iron, these devices may not be
manufactured to a high standard.

=== DS3231 ZS-042 ===

This module contains the RTC and an HK24C32 EEPROM. It tends
to ship with a CR2032 battery and, as the per
advice of many web sites, it's important to desolder
the charge feature of the module (see schematic).

By default the EEPROM content is
<code>
./mcp24 1 0x57 -d
EEPROM FOUND AT 0x0057
DUMP
[0000] 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F 50 |ABCDEFGHIJKLMNOP|
[0010] 51 52 53 54 55 56 57 58 59 5A FF FF FF FF FF FF |QRSTUVWXYZ......|
</code>