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Technical Manual
CPU-44
1.3.10 Parameter RAM and Real-Time Clock
The real-time clock is designed with the MK48T18 timekeeper RAM. It combines a 8Kx8 CMOS SRAM
(parameter RAM), a bytewide accessible real-time clock, a crystal, and a long-life lithium battery, all in
one package.
1.3.11 VIC Timer
The VIC contains a timer that can be programmed to output a periodic wave form on LIRQ2. The available
frequencies are 50 Hz, 100 Hz, and 1000 Hz. The VIC timer is typically used as a tick timer for multi-tasking operating systems.
1.3.12 Watchdog Timer
The watchdog timer monitors the activity of the microprocessor. If the microprocessor does not access the
watchdog timer within the time-out period of 100 ms or 1.6 s, a reset pulse is generated. After reset, the
watchdog timer is disabled. The normal time-out period of 100 ms/1.6 s becomes effective after the first
access to the watchdog timer.
The left decimal point of the hex display located at the front panel is illuminated to indicate a watchdog reset. This watchdog indicator is only cleared by power-up reset, the reset switch, a VMEbus SYSRESET, or
a VIC remote reset.
The state of the watchdog indicator can be read by software using bit PA7 of the system control register located in the system CIO.
1.3.13 Status Display
The CPU-44 features a seven-segment display on the front panel and displays hexadecimal values from 0 F.
This status display ($FEC3.0000) is designed as a read / write register and uses the least significant nibble
of the byte.
The right decimal point of the hex display is controlled by PA0 of the system control register. The right
decimal point is used as an initialization status by the monitor program. After reset the right decimal point
is illuminated. RMon switches the decimal point off before the user program in the user EPROM is called.
The LED next to the reset button shows the status of the CPU. It is illuminated when the CPU is running
and it is off when the CPU is halted.
1.3.14 Reset
Reset may be initiated by six sources:
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supply voltage drop below 4.75 V or power-up
reset switch on the front panel
VMEbus SYSRESET
049-13856-101 Rev A1
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