Table of Contents
Advertisement
PIC16C55 Pin functions:
RB0
RB1
RB2
K
y b
e
o a r
RB3
sense
inputs
RB4
RB5
RB6
RB7
PI C
1 6 C 5 5
RC0
RC1
RC2
K
y b
e
o a r
RC3
scan outputs
RC4
(active=L)
RC5
RC6
RC7
Image 8-4
Pic16C55 pin fuctions
RC5 Sequences Extended
R C 5
q
s e
u e n c e s
Command String
24,9 ms
Image 8-5
RC5 sequences
During the idle time of the local control panel, the IC PIC is in the sleep mode and all scan outputs are low.
Any key action will discharge the RESET timing capacitor C1 through the involved sense input pull up resistor (R1..R8). When the
C1 voltage drops to 0.15VDD, the PIC resets and puts the scan outputs in the Hi_Z state. The capacitor C1 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, the scan pin is put to low momentarily, during which time the 8
sense inputs are read and stored in the memory. After that, key debounce is done by a 20ms delay loop.
Next, the keyboard matrix is scanned: one after another the columns are forced to low through the scan pins RC0..RC7, and each
time, the bit pattern of the column is read through the sense inputs RB0..RB7.
Q1 is the output buffer and ensures the output is inverted on its route to the output connector J1, D1 is a protection diode for the
output logic, and D2 protects I2 from inverse voltage.
The whole matrix is always scanned to detect simultaneously pressed keys, 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:
R5976820 SLM R12+ PERFORMER 08/03/2005
+
VDD
Reset In
MCLR/VPP
d
Osc. In
Osc. Out
RC5 code
RA0
d
RA1
Not used
RA2
Not used
Jumper scan out
RA3
(active=L)
VSS
Command String is repeated every 114 ms
114 ms
Command String
1
1
0
0
0
1
0
1
2 x S tart
T og gle
5 x A ddress
B it
B it
B its
The Burs
t F
q
y i
3 6 k H
r e
u e n c
s
27.8u s
Pin functions:
VDD: Power Supply
Vss: Ground connection
Oscillator : Use of a 400kHz Ceramic resonator with 2
load capacitors of 82pF.
MCLR Reset Input : to be activated in 2 cases:
- Power On: all memory locations are initialised.
- Awake from sleep: keyboard matrix is scanned,
key entries are processed, and the device goes
back to sleep.
RA0: Output to Controller : active=H
RB0..RB7 : Keyboard Sense Inputs
RC0..RC7 : Keyboard Scan Outputs
active=low
The RC-5 Code
In the RC-5 standard a bi-phase coding (Coding: a
1
0
0
0
1
0
rising edge within a time window is equivalent to a "1",
a falling edge represents a "0") is applied. The carrier
frequency is fixed at 36 kHz.
The transmission of a word begins with two start bits,
followed by a toggle bit. The toggle bit changes its
6 x C om m and
B its
value at each key operation. With this change an
interruption of the transmission link can be
distinguished from a multiple key pressing. The 5
address bits address the device to be controlled, the
3 3 % d
i t h
t y
y
l
z
w
a
u
c
c
e
command bits contain the information to be transmitted.
,
Each bit in a data word consists of a burst of 32 pulses
with a repetition rate of 36 kHz. The equivalent times
are shown on the puls diagram.
8. Local Keypad & LCD Display
Command String
45
Advertisement
Table of Contents
