AN1759 datasheet(13/24 Pages) FREESCALE

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Application Note

MC68HC705J1A Software Interface

AN1759

MC68HC705J1A Software Interface

I/O driving or manipulation is the process of toggling I/O pins with

software instructions to create a certain hardware peripheral. The HC05

CPU provides special instructions specifically to manipulate single

I/O pins.

Five subroutines were created to provide an easy application

programming interface (API). These routines are:

• START_SER — Sends out a start condition on the bus

• STOP_SER — Sends out a stop condition on the bus

• TXD — The master takes the contents of AccA and transmits it

MSB first to the DS1307. The master also checks for

acknowledgement from the DS1307.

• RXD — After the master addresses the DS1307 with its

identification code and the read bit, the DS1307 transmits a byte

of data back to the master. This routine reads that byte and puts it

into AccA. The master also generates an acknowledgment back to

the DS1307.

• RXD_LAST — This routine is just like RXD but it is used for the

last byte read from the DS1307. It does not generate an

acknowledgment back to the DS1307.

The flowcharts for the DS1620 serial I/O drivers are shown in

Flowcharts for the Test Interface

. These routines were written

especially for the DS1307 and may not be able to properly drive other

MCU peripherals with 2-wire serial buses.

A typical application would use the SQW/OUT pin on the DS1307. When

configuring this pin for a 1-Hz signal, feed the signal to the IRQ pin of an

MCU. An interrupt routine can be created to read the contents of the

DS1307 every time a 1-Hz signal hits the IRQ pin. This should take

minimal CPU bandwidth and provide the user an easy way to retrieve

time and date information.

The main test routine was written to verify the bus interface between the

DS1307 and the J1A. It writes a known date and time into the DS1307

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AN1759 Datasheet(PDF) 13 Page - Freescale Semiconductor, Inc