Barco SLM R12 Plus, Service Manual, Page: 43 / 281

7. IR Transmitter RC-5 Coded R763569
Enhancements
W4 W3 W2 W1
Enhancements:
Jumper W1 'Address Mode' Installed?
- Yes: command send with free address
- No: command send with fixed address
Jumper W2 'Address Entry' Installed?
- Yes: entering address with 2 digits (0..31)
- No: entering address with 1 digit (0..9)
Jumper W3 'Extend' Installed?
- Yes: extended
- No: Standard RC5 protocol
Jumper W4 : further expansion
Image 7-10
Remote control enhancements
7.5 Technical Description
Introduction
The Infra Red Remote control is built around an EPROM-Based 8-Bit CMOS Microcontroller with hardware selectable enhance-
ments.
Operation
During the idle time of the RCU, the IC PIC is in the sleep mode and all scan outputs are low. Any key action will discharge the
RESET timing capacitor C3 through the involved sense input pull up resistor (R1..R8). When the C3 voltage drops to 0.15VDD, the
PIC resets and puts the scan outputs in the Hi_Z state. The capacitor C3 recharges through the resistor R9 and when the 0.15VDD
is reached, the PIC starts running. Since this is a reset from sleep, a ’warm reset’ procedure is started, which reads "IN" the option
jumpers. Pin RB7 is put high to bias the pull up resistor R12. One after another, pins RB0...RB6 generate 1, 2, 4, 8,...64 pulses
respectively, which are counted by the PIC. The totalled counts reveal which option jumpers are installed. After that, a delay loop is
initiated to obtain a total key debounce of 20 ms. Next, the keyboard matrix is scanned: one after another the rows are forced to low
through the scan pins RB0..RB7, and each time, the column pattern is read through the sense inputs RC0..RC7. The whole matrix
is always scanned to detect simultaneously key activations, in which case the scan results are ignored. The scan pulses only last
20 oscillator periods, short enough to have no influence on the reset pin voltage.
Depending on which key was pressed, the following actions can be taken:
1. Address key (S43): The ’ADDR’ command is transmitted along with the ’always listen’ address value (address ’0’). A 5 seconds
countdown starts, during which 1 or 2 numeric key entries are expected. Each numeric key entry is followed by a 260 ms holdoff
and restarts the countdown, but now for 2 seconds. If the initial time window elapses without a numeric key entry, or if an invalid
address (e.g. >31) is entered, the RCU address is reset to the ’always listen’ value.
2. Laser key (S41): If the option, pin RB6, is activated (RCU type is executive) the RA3 pin is switched high and no code is trans-
mitted.
3. Other keys: The corresponding command is transmitted along with the address last entered. The command bits are NOT related
to the matrix co-ordinates: the key number, which is =row*8+column, is used to select the appropriate command from a look up
table. (e.g. Button S41 pressed - Key number=2(row)x8+7(colomn)=23)
After transmitting, the keyboard is scanned once more to detect if a key is still pressed. This keeps the repetition rate controllable
at exactly 115 ms, because the reset timing is offside now.
Power supply
The IC1 needs to run from the +3V Nominal type (2 x 1.5V cells).
IR LED drive
The transistors Q1 and Q2 drive the IR LED’s in a constant current figuration. An emitter-follower Q5, which is following the pulse
output of IC1, provides the drive current for the bases of the 2 transistors. The base signal of Q5 is stabilized in amplitude. The
capacitor C5 acts as a reservoir for supplying the high current pulses (up to 400 mA in total) that could not be drawn from the 3V
battery on its own, due to the internal resistance.
R5976820 SLM R12+ PERFORMER 08/03/2005 41