#42, M1S: RTC and NVRAM With Backup

Function: Real-time clock and non-volatile memory with backup battery and interrupt output

Form factor: M1S

Category: Input/output module

Special needs: ---

Power requirements: 5V/10mA

Mates with: #19, #20, #21 (limited use), #37

See also: ---

Details

Tibbit #42 is based on the DS3234 IC from Maxim Integrated. This is a temperature-compensated high-accuracy RTC with non-volatile memory. Refer to the Maxim Integrated datasheet for operation details.

The DS3234 RTC has an –INT/SQW pin, which can be set to trigger at a predefined date/time or output a square wave signal. The –INT/SQW is available to the outside world through line IO1. –INT/SQW is also accessible from the CPU. The line is multiplexed with the DOUT signal of the DS3234. The multiplexor is controlled by the state of the –CS line. When –CS is LOW, thus indicating that an SPI transaction is in progress, the multiplexor selects the DOUT line. When –CS is HIGH, the multiplexor selects the –INT/SQW signal. Therefore, it is only possible to gauge the –INT/SQW state when the SPI bus is idle.

Tibbit #42 carries a backup battery, which powers the RTC when the main +5V supply is off.

LEDs

There are three red and one green LED. The red LEDs are connected to the –CS, SCLK, and MOSI lines. The green LED is connected to the MISO/–INT line.

Sample Project

The use of Tibbit #42 is illustrated by a Tibbo BASIC test project. You can find it here: https://github.com/tibbotech/CA-Test-Tibbit-42.

The non-volatile memory of the DS3234 can be used from within the STG (settings) library. Projects often have parameters (settings) that change too often to be stored in the EEPROM, yet must be preserved even when the power is off. The non-volatile memory of this Tibbit offers a perfect storage for such parameters.