2010ECL-NYC SERIES SIGNAL MONITOR
OPERATIONS MANUAL
Eberle Design Inc.
Page 27
Section 6
CIRCUIT OPERATION
6.1 INTRODUCTION
The Signal Monitor uses a dual microprocessor architecture consisting of an 68HC11D0 main
microprocessor unit (MPU) and a Microchip PIC17F242 based RMS-Engine. The RMS-
Engine is a dedicated single-chip high speed microcontroller used to sample the AC field
inputs and calculate the true Root Mean Squared (RMS) voltage. The 68HC11D0 main
microprocessor uses a high speed synchronous serial I/O system called the Serial Peripheral
Interface (SPI) to exchange data with the peripheral circuit blocks. It controls all functions of
the unit except for those of the RMS-Engine.
6.2 MAIN MPU LOGIC
The 68HC11D0 main microprocessor (U13) operates in the Expanded Multiplexed mode
which allows for external memory devices. The program firmware is contained in the
29F010B CMOS Flash device (U11) and program data storage is contained in the SRM2264
8Kx8 static RAM (U16). The expanded address and data buss is used to link the memory
devices with the microprocessor. A 74HC137 (U14) selector also resides on the buss to
generate chip select signals for the SPI devices.
6.3 SERIAL PERIPHERAL INTERFACE (SPI)
The Serial Peripheral Interface (SPI) is a high speed synchronous serial I/O system used to
interconnect the main microprocessor to the following circuit blocks: EEprom (U21), Real
Time Clock (U29), 24Vdc Logic Processor (U41), Display Multiplexer (U1), Program Card
and Switch inputs (U25.4), and the RMS-Engine (U37).
Data is clocked out of the main microprocessor on the MOSI pin (U13.18) while data is
clocked in on the MISO pin (U13.17). The SCLK signal (U13.20) provides the synchronous
clock. A peripheral device must be selected by U14 before SPI transfers may take place.
6.4 INTERNAL MPU WATCHDOG
Circuit U4A and U4B comprise the internal MPU Watchdog circuit. If this circuit does receive
an input from the main microprocessor for at least 325 ms, the circuit will trigger and force
the Output relay to the fault mode, enable the Stop-Time output, and illuminate the
DIAGNOSTIC indicator. This indicates that the microprocessor has failed to operate its
program loop. Under normal conditions the microprocessor will clock this circuit every 20 ms.
If jumper E13 is installed this fault mode will only be reset by a power down cycle.
6.5 EEPROM MEMORY
The 25C640 Serial EEprom (U21) device provides 8192 bytes of nonvolatile memory. It is
interfaced to the main microprocessor through the SPI port. No battery is required to maintain
the data in this device.
6.6 24VDC LOGIC INPUTS
The Cabinet 24VDC input, CU Watchdog input, and External/Manual Reset inputs are
processed by a PIC16F687 microprocessor U41. Opto-couplers U28, U31, U36, and U38
provide electrical isolation between Logic Ground and Neutral.
