Motorola M68HC11EVBD, User Manual

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HARDWARE PREPARATION AND INSTALLATION
2-14 M68HC11EVBU/D
2.4 REAL-TIME CLOCK, RAM, SERIAL INTERFACE PERIPHERAL
A user-supplied HCMOS real-time clock, RAM, and serial interface peripheral device
(MC68HC68T1) can be installed on the EVBU at location U5. The MC68HC68T1 peripheral
device contains a real-time clock/calendar, a 32 x 8 static RAM, and a synchronous, serial, three
wire interface for MCU communications. Operating in a burst mode, successive clock or RAM
locations can be read or written using only a single starting address An on-chip oscillator allows
acceptance of a selectable crystal frequency or the device can be programmed to accept a 50/60
Hz line input frequency.
Features of the MC68HC68T1 peripheral device are as follows:
•
Full clock features – seconds, minutes, hours (AM/PM), day-of-week, date, month,
year (0-99), auto leap year
•
32 word by 8-bit RAM
•
Direct interface to Motorola serial peripheral interface (SPI)
•
Minimum time-keeping voltage 2.2 V
•
Burst mode for reading/writing successive addresses in clock or RAM
•
Selectable crystal or 50/60 Hz line input
•
Binary-coded-decimal (BCD) data contained in registers
•
Buffered clock output for driving CPU clock, timer, colon, or liquid crystal display
(LCD) backplane
•
Power-on reset with first-time-up flag
•
Freeze circuit eliminates software overhead during a clock read
•
Three independent interrupt modes – alarm, periodic, or power-down sense
•
CPU reset output – provides orderly power up/down
•
Watchdog circuit
Refer to the MC68HC68T1 Real-Time Clock plus RAM with Serial Interface data sheet
(MC68HC68T1/D) for additional device information.
In addition to the MC68HC68T1 circuitry, diode jumpers (D1-D4) and test points (TP1-TP6) are
also included. The following paragraphs describes the purposes of the diode jumpers and test
points in conjunction with the MC68HC68T1 device installed in socket location U5.