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b101101011011011
Joined: 03 Sep 2007
Posts: 7
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| Understanding-Generating PS/2 keyboard signal with PIC |
 Posted: Wed Sep 05, 2007 11:38 am |
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Hello,
I need a help to project a circuit to running in paralell interface with a keyboard PS/2.
I read about PS/2 protocoll. I understood that the computer generates one clock for the keyboard. Its realy?
In pinage from PS/2 cable, i read clock signal, and my oscilloscope show AC signal, and not DC signal. Its correct?
I am usign a source code that I found here in CCS forum and google. But, its not works correct. 
Please, help. I need generate keyboard commands in PIC to PC.
Lock my code:
| Code: |
#include <16F628A.h>
#use delay (clock=4000000)
#fuses INTRC_IO, NOWDT, NOPUT, NOBROWNOUT, NOMCLR, NOLVP, NOPROTECT
#define CLOCK PIN_A1
#define DATA PIN_B1
#define KEYCLK CLOCK
#define KEYDATA DATA
unsigned char convert_ascci_to_scancode(unsigned char c){
unsigned char scancode;
if (c == 'a' || c == 'A') {scancode = 0x1c;}
else if (c == 'b' || c == 'B') {scancode = 0x32;}
else if (c == 'c' || c == 'C') {scancode = 0x21;}
else if (c == 'd' || c == 'D') {scancode = 0x23;}
else if (c == 'e' || c == 'E') {scancode = 0x24;}
else if (c == 'f' || c == 'F') {scancode = 0x2b;}
else if (c == 'g' || c == 'G') {scancode = 0x34;}
else if (c == 'h' || c == 'H') {scancode = 0x33;}
else if (c == 'i' || c == 'I') {scancode = 0x43;}
else if (c == 'j' || c == 'J') {scancode = 0x3b;}
else if (c == 'k' || c == 'K') {scancode = 0x42;}
else if (c == 'l' || c == 'L') {scancode = 0x4b;}
else if (c == 'm' || c == 'M') {scancode = 0x3a;}
else if (c == 'n' || c == 'N') {scancode = 0x31;}
else if (c == 'o' || c == 'O') {scancode = 0x44;}
else if (c == 'p' || c == 'P') {scancode = 0x4d;}
else if (c == 'q' || c == 'Q') {scancode = 0x15;}
else if (c == 'r' || c == 'R') {scancode = 0x2d;}
else if (c == 's' || c == 'S') {scancode = 0x1b;}
else if (c == 't' || c == 't') {scancode = 0x2c;}
else if (c == 'u' || c == 'U') {scancode = 0x3c;}
else if (c == 'v' || c == 'V') {scancode = 0x2a;}
else if (c == 'w' || c == 'W') {scancode = 0x1d;}
else if (c == 'x' || c == 'X') {scancode = 0x22;}
else if (c == 'y' || c == 'Y') {scancode = 0x35;}
else if (c == 'z' || c == 'Z') {scancode = 0x1a;}
else if (c == '0') {scancode = 0x45;}
else if (c == '1') {scancode = 0x16;}
else if (c == '2') {scancode = 0x1e;}
else if (c == '3') {scancode = 0x26;}
else if (c == '4') {scancode = 0x25;}
else if (c == '5') {scancode = 0x2e;}
else if (c == '6') {scancode = 0x36;}
else if (c == '7') {scancode = 0x3d;}
else if (c == '8') {scancode = 0x3e;}
else if (c == '9') {scancode = 0x46;}
else if (c == '/') {scancode = 0x5a;} // ENTER
else if (c == ' ') {scancode = 0x29;} // ESPACIO
else if (c == '>') {scancode = 0x0d;} // TABULADOR
else if (c == '<') {scancode = 0x66;} // BORRADOR
else if (c == '$') {scancode = 0x58;} // TAG DE MAYUSCULA $m$yuscula
else if (c == '-') {scancode = 0x4a;} // -_
else {scancode = 0x29;} // Cualquier otra cosa ESPACIO
return scancode;
}
void sendByte(byte b)
{
byte a=0;
byte p = 0;
boolean t = 0;
disable_interrupts(GLOBAL);
output_low(KEYCLK);
delay_us(80);
output_low(KEYDATA);
output_high(KEYCLK);
input(KEYCLK);
for(a=0; a<8; a++)
{
while(input(KEYCLK) == 1); //wait for 0
t = bit_test(b,a);
output_bit(KEYDATA, t);
if(t)
p++;
while(input(KEYCLK) == 0); //wait for 1
}
while(input(KEYCLK) == 1); //wait for 0
t = bit_test(p,0);
t = ~t;
while(input(KEYCLK) == 0); //wait for 1
output_bit(KEYDATA, t); // input(KEYDATA);
while(input(KEYCLK) == 1); //wait for 0
output_float(KEYDATA);
enable_interrupts(GLOBAL);
}
main()
{
int i=0;
unsigned char k=0;
set_tris_a(0b11111111);
set_tris_b(0b00000000);
output_b(0x00);
input(CLOCK);
delay_ms(100);
ext_int_edge(H_to_L);
enable_interrupts(INT_EXT);
enable_interrupts(GLOBAL);
while(1)
{
sendByte(convert_ascci_to_scancode('a'));
delay_ms(500);
sendByte(convert_ascci_to_scancode('B'));
delay_ms(500);
sendByte(convert_ascci_to_scancode('C'));
delay_ms(500);
sendByte(convert_ascci_to_scancode('d'));
delay_ms(500);
sendByte(convert_ascci_to_scancode('e'));
delay_ms(500);
delay_ms(2000);
}
}
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amcfall
Joined: 20 Oct 2005
Posts: 44
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| Posted: Thu Sep 06, 2007 8:55 am |
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Not sure what you're doing here, need some more info. What does "a circuit to running in paralell interface with a keyboard PS/2 " mean?
The clock is generated by the keyboard if I remember correctly. If you are emulating a keyboard you will need to generate the clock. It looks like you're waiting for the clock but are trying to act as a keyboard.
I wrote my implementation (owned by the company I work for so I cannot post any of it) based mostly on this site:
http://www.computer-engineering.org/ps2protocol/
Avery |
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b101101011011011
Joined: 03 Sep 2007
Posts: 7
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| Posted: Thu Sep 06, 2007 7:37 pm |
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Hello amcfall!
Thanks for look this topic.
For more informations i make a picture schematic.
See:
http://img160.imageshack.us/img160/9578/esquemabv1.jpg
My doubt is about CLOCK generation... I use a clock from keyboard? OR need to generate a PWM signal with 10 Khz from my PIC circuit?
Thanks amcfall. |
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Guest
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| Posted: Fri Sep 07, 2007 1:55 am |
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The PS2 interface is a type of the synchron serial IF. Becouse of the muster - who want to send - must generate the synchron clock for associated data.
NOT PWM !
If I understand, you must send data from PIC OR PS2 on paralellised cable. If you push key in keyboard, the keyboard generate clock, if a PIC want sending anything, the PIC will generate the clock !!! |
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arunb
Joined: 08 Sep 2003
Posts: 492
Location: India
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| RE: |
| Posted: Fri Sep 07, 2007 2:35 am |
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Hi,
What if both PIC and keyboard send character...both will generate clock ??
arunb |
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Guest
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| Posted: Fri Sep 07, 2007 4:15 am |
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I think the problem is a keyboard response in the clock-data bus.
The keyboar is not ready to a multi master enviroment.
If the PIC use the clock and data line (quasi bus) both the PC and the keybord is a receiver. But the keyboard will not recognise the event and make error. PIC will not recognise from where get it. From PC? or from Keyboard? The communication protocoll is ready for one PC and one kbd connection. |
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Guest
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| Posted: Fri Sep 07, 2007 4:20 am |
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The solution:
KBD->PIC->PC
PIC receive KBD scan codes and transmit to PC (repeater), and if PIC must send anithing, it does too. |
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Ttelmah
Guest
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| Posted: Fri Sep 07, 2007 4:30 am |
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The clock, and data lines, are 'open collector' drives. There are pull-up resistors, to bring the signals to 5v, when not driven, and a transistor to pull the signal down when a drive is needed. These need to be implemented, like the I2C bus (when software driven) on the PIC. What you do, is set the output latch register on the PIC pins, to '0', and then turn the TRIS register 'on', when you want to drive the signal low (enables the output driver), and 'off' when you want the signal to be pulled up. This way, the other device, can pull the signal 'down' at any time, and not cause damage. To do this, you will need to use fixed, or fast_io mode on these pins.
The slave device must monitor the lines before trying to send. The host will pull the clock low, to inhibit slave communication, before trying to send. The slave is required to check that the clock _is_ high, and stays high for at least 50uSec, before it is allowed to start sending. At _any_ time, the host can pull the clock low to abort the communication. Hence the slave _must_ check that the pin actually goes high, when it releases the clock on each bit. If the transmission is inhibited before 11 clcok bits of the packet have been sent, the slave ios required to send again latter.
Best Wishes |
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