78M6618 Data Sheet
DS_6618_005
1.12 Real-Time Clock (RTC)
The RTC circuit is driven directly by the crystal oscillator. The RTC consists of a counter chain and output
registers. The counter chain consists of registers for seconds, minutes, hours, day of week, day of
month, month, and year (including leap years). See the 78M6618 Programmer’s Reference Manual for
more information regarding the use of the 78M6618 RTC.
1.13 Hardware Watchdog Timer
In addition to the basic watchdog timer included in the 80515 MPU, an
V1
independent, robust, fixed-duration, watchdog timer (WDT) is included in
V3P3
V3P3 - 10mV
WDT dis-
abled
the device. It uses the crystal oscillator as its time base and must be
refreshed by the MPU firmware at least every 1.5 seconds. When not
refreshed on time the WDT overflows, and the part is reset as if the RESET
pin were pulled high, except that the IORAM bits will be maintained. 4096
oscillator cycles (or 125 ms) after the WDT overflow, the MPU will be
launched from program address 0x0000. Asserting ICE_E will deactivate
the WDT.
V3P3 -
400mV
Normal
operation,
WDT
enabled
VBIAS
The WDT can also be disabled by tying the V1 pin to V3P3. This also
deactivates V1 power fault detection. Since there is no method in firmware
to disable the crystal oscillator or the WDT, it is guaranteed that whatever
state the part might find itself in, upon watchdog overflow, the part will be
reset to a known state.
Battery
modes
0V
Figure 3: Functions Defined by V1
1.14 Temperature Sensor
The device includes an on-chip temperature sensor for determining the temperature of the bandgap re-
ference. The primary use of the temperature data is to determine the magnitude of compensation required
to offset the thermal drift in the system. See the 78M6618 Programmer’s Reference Manual for more
information regarding the use of the 78M6618 Temperature Sensor.
1.15 General Purpose Digital I/O
The 78M6618 includes up to 19 pins of general-purpose digital I/O. When configured as inputs, these
pins are 5V compatible (no current-limiting resistors are needed). On reset or power-up, all DIO pins are
inputs until they are configured for the desired direction under MPU control. The Digital I/O pins can be
categorized as follows:
•
•
•
•
•
DIO1/OPT_RX, DIO2/OPT_TX
DIO3
DIO4/SEG24 -- DIO11/SEG31 (8 pins) LCD/DIO pins
DIO13/SEG33 -- DIO19/SEG39 (7 pins) LCD/DIO pins
(2 pins) UART/DIO pin
(1 pin ) Dedicated DIO pin
DIO43/SEG63
(1 pin ) LCD/DIO pin
10
Rev. 1.4
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
