Real Time Clock - Technologic Systems TS-5700 User Manual

TS-5700 User's Manual Technologic Systems http://embeddedARM.com/

12 Real Time Clock

The TS-5700 has a standard PC compatible real-time clock (RTC) that is built into the Elan520 CPU. This clock
has no battery-backup, which means it is volatile, and must be initialized after power is applied. If a non-volatile
battery-backed RTC is required, the TS-5620 peripheral board can be added to provide this capability. The TS-
5620 is a very low-cost option that is only 1.1 x 3.5 inches (2.8 x 9.0 cm) and uses an ST Micro M48T86PC1
module for the real-time clock function. This module contains the lithium battery, 32.768 kHz crystal, and a RTC
chip with 114 bytes of battery-backed CMOS RAM. It is guaranteed to maintain clock operation for a minimum of
10 years in the absence of power.
Both the internal RTC and the TS-5620 RTC are totally compatible with the Motorola 146818 chip used in the
original PC. It is located at the standard PC I/O addresses of Hex 070 and 071. The top 48 bytes (index 50h
through 7Fh) are not used by the BIOS and are available for user applications. However, since the TS-5700
uses an EEPROM to make this data non-volatile, a special method must be used to make any user data non-
volatile. If you wish to use this area for non-volatile storage, contact Technologic Systems for details.
The CMOS RAM that is located inside the RTC chip is used to hold all of the BIOS set-up parameters. This
RAM is always non-volatile even when using the internal RTC. All of the set-up parameters are stored in a non-
volatile EEPROM chip. The data stored in the EEPROM is copied into the CMOS RAM during every boot cycle.
This is all totally transparent and appears to operate as a standard CMOS set-up RAM.
schematic for the TS-5620 is posted on our website. The TS-5620 design only uses two chips. This circuitry
The
can be freely used on any customer peripheral board design if the battery-backed RTC feature is necessary.
The TS-5700 internal RTC is capable of generating a square wave output function with a period of 500 mSec to
122 uSec. The TS-5620 RTC does not have access to IRQ8 and can not implement this function. The internal
RTC square wave output pin is connected to IRQ8 on the processor, and can be used to generate periodic
interrupts. The keypad example code uses this function to generate interrupts at a 256 Hz rate.
http://www.embeddedARM.com/old/downloads/KEYPAD.ZIP
21 5/2009