User manual

Page 4
Document No. 80-15151 Issue 6 HEBER LTD
5 CIRCUIT OPERATION
This section describes how some elements of the circuit operate and their capabilities and limitations.
A subsequent section deals with how the various capabilities of the board are used to implement
specific amusement machine functions.
5.1 Power Supplies
The Power Input to the board is on P3. There are 3 input voltages required, +12V, -12V and 36V or
48V for the lamp multiplex.
The +12V supply is fused by F1 (3.15A) as it comes on the board. From the un-fused (input) side, the
+12V is distributed to the Reel Connector, P7 where it may be used to provide the supply for the
Stepper Motors.
From the fused side, the +12V is used for the following:
• Regulated via U15 to provide the Vcc (+5V) supply for the board. This will draw up to 250mA from
the +12V rail.
• To provide the Power Supply for the Stereo Audio Amplifier, U32. The load current drawn by this
will depend on the audio volume, etc. but is not likely to exceed an average of about 200mA.
• Monitored by U16B to detect imminent failure of the +5V supply and cause a Level 7 (Non-
Maskable) Interrupt, NMI-. The interrupt will occur if the +12V supply drops below approximately
7.8V.
• To provide the Power Supply for the multiplexed LED drive circuits. With 32 LED digits fitted and
all having all segments illuminated, the current drain is likely to be between 400mA and 550mA.
• Distributed to various connectors, P1, P2, P8, P9, P12 and P14 for optional use by external
circuits.
When connecting external loads to the Fused +12V outputs on P1, P2, P8, P9, P12 and P14 make
sure that the total current drawn is within the rating of fuse F1 (3.15A), making due allowances for the
other loads as described above.
The –12V supply input provides the negative supply for the 1488 RS232 Transmitter Buffer, U33, and
the –12V supply required on the DATAPORT Connector, P2.
The Lamp Multiplex supply should be +36V or +48V, depending upon the duty cycle employed by the
software. See Section 6.10, “Using Multiplexed Lamps” for more information.
Transient suppressers (Tranzorbs) are fitted on the +12V supply (fused side), -12V supply and Vcc to
protect these lines against any overvoltage.
5.2 Reset and Power Fail Detection
TL7705 device, U17, (see Schematic Sheet 10 - Reset/Battery/RS232), provides the system reset. At
power up, the system is held in a reset state (RESET- low, RESET high) for about 5 seconds. This
time is determined by C14. The processor may initiate a full hardware reset at any time by asserting
Port B, pin 0 (PB0) low, which will trigger the TL7705 via the RESIN- pin. The RESET lines will also be
immediately asserted by the TL7705 if the Vcc line drops below 4.75V.
While the system is in a reset state, i.e. RESET- is low, a red LED, LD1, is illuminated.
The power fail detection is a simple threshold detection on the 12V rail using one section of the quad
comparator LM339 (U16B), see Schematic Sheet 9 - IO Connectors.
When the +12V input falls below a threshold of approximately 7.8V, the output of the comparator goes
low which causes a Level 7 interrupt (NMI) to the processor. This will occur BEFORE the 7805
regulator drops out of regulation and the Vcc line starts to drop, thus giving the processor a period of
time to react before the RESET is asserted by the TL7705, U17. The main purpose of giving the