Post by thread:key matrix scanning

> somebody please tell me whether a > X-Y key matrix is efficient, if i > am checking for key combinations > rather than single-key presses. > i ask because the 16c84 has only 1k > of code space, and key matrix > scanning consumes a lot of space. Matrix scanning doesn't have to use a lot of space; it depends what you're looking for. If you have, e.g., a full 4x8 matrix and you want to look for all possible key combinations (and you've put in diodes as needed) your best bet is probably do do something like this: movlw 1 movwf PORTA call Delay movf PORTB,w movwf ROW0 movlw 2 movwf PORTA call Delay movf PORTB,w movwf ROW1 movlw 4 movwf PORTA call Delay movf PORTB,w movwf ROW2 movlw 8 movwf PORTA call Delay movf PORTB,w movwf ROW3 Twenty words of code space (plus the delay routine); 4 bytes of registers. Doing a decent debounce would probably require another 4 bytes; a better debounce (if you're calling the routine often enough to require one) would probably take 8 to 16 bytes. Note, btw, that you can replace the "delays" above with debounce code if desired (which will take a few microseconds to execute, giving the next keyboard row time to settle). Is the above approach too register-hungry for you, or are you looking for something else?

At 11:18 AM 8/15/97 -0700, Ravindra Divekar wrote: >somebody please tell me whether a >X-Y key matrix is efficient, if i >am checking for key combinations >rather than single-key presses. >i ask because the 16c84 has only 1k >of code space, and key matrix >scanning consumes a lot of space. I would go with a bitfield instead. Like 'set of byte' in Pascal, so if you have say 12 keys to deal with like on a numeric keypad for a phone (0-9,#,*) then it would take 12 bits. One bit per key pressed. 123456789*0# 110110100001 would translate to 1,2,4,5,7,# You see what I mean? --- Unknown

Ravindra Divekar wrote: > > somebody please tell me whether a > X-Y key matrix is efficient, if i > am checking for key combinations > rather than single-key presses. > i ask because the 16c84 has only 1k > of code space, and key matrix > scanning consumes a lot of space. > > --Ravindra You should be aware that people may not leave the previos key before pressing next key.

Ravindra Divekar wrote: > > somebody please tell me whether a > X-Y key matrix is efficient, if i > am checking for key combinations > rather than single-key presses. > i ask because the 16c84 has only 1k > of code space, and key matrix > scanning consumes a lot of space. > > --Ravindra Instead of using diodes try to use transistors. *---------------* I I /-------\ I I I I I u-Amp I I I I I \-------/ I I - I I BC547 I plate /--I--\ /-------\ I I I I I I I *--I I----*--I--I--I I Vdd I I I I I I \I/ I I I I I \--I--/ \-------/ I III I I - I 1kI I I I I III I I I I I I I *-----* I I I pulses I I /-------\ I I I --- I I I I I I I I I I -- -- I I I \-------/ I I I I *---------------*---------------* Try to messure the distance between the plates with varios frequences and Amp's. Rgds,

If you use a xy matrix then diodes are required for each switch to check for multiple key presses otherwise it works ok (fell in to that one myself when reading personality jumpers) If you do the code in a loop then the scan code can be quite small it only requires a single decrement counter (for the colums) and the FSR to store the rows in consecutive memory locations. Go round the loop onece for each colum. Steve.....

Ravindra Divekar wrote: > > somebody please tell me whether a > X-Y key matrix is efficient, if i > am checking for key combinations > rather than single-key presses. > i ask because the 16c84 has only 1k > of code space, and key matrix > scanning consumes a lot of space. > > --Ravindra It is perfect for the job. If, for instance you have a 4X4 keypad, you can use 4 inputs and 4 outputs on the same port. The port value will be unique for *any* combination of keys. Moreover, if your debounce routine validates the key(s) upon leaving the key, you can also have special meanings attached to keys that are pressed for longer than, say, a second. -- Friendly Regards Tjaart van der Walt spam_OUTtjaartTakeThisOuTwasp.co.za ________________________________________________________ | WASP International http://wasp.co.za | | R&D Engineer : GSM peripheral services development | |Vehicle tracking | Telemetry systems | GSM data transfer| |Voice : +27-(0)11-622-8686 | Fax : +27-(0)11-622-8973 | | WGS-84 : 26010.52'S 28006.19'E | |________________________________________________________|

On Fri, 15 Aug 1997, Ravindra Divekar wrote: > somebody please tell me whether a > X-Y key matrix is efficient, if i > am checking for key combinations > rather than single-key presses. > i ask because the 16c84 has only 1k > of code space, and key matrix > scanning consumes a lot of space. > PTM: Good guestion ! I have been after a cheap chip for scanning keyboard. Preferably I2C to make keyboard scanning. There is this 74xx922, 74xx923, but it is expensive and for only 16 or 20 keys. So far I'm going to use 74xx137 for scanning. The same chip can be used to scan the LED-display too. 1:5 MUX for the display works fine if you use Hi-Bright LED's. PIC's lack of indexed addressing makes thins a bit difficult. ________ _______ | |....| | 5 ___________ |PIC |....|73137|-------/------|5x6 keyb | | |....| |- | | | | | |- | | -------- ------ - ----------- | 5 ||||| -----/--------------------------||||| « | |||||<-transistors here | 5 ______ 7 ___________ ----/----|4511 |------/------|LED-displ | ------ ----------- (use about 10k resistors to Vcc in the keyboard) Another thing is that I have not found a cheap LED-display controller that can show the wild codes (hex 0x0A..0x0F) too or full ASCII. I prefer I2C but everything goes. -------------------------------------------------------------------------- PTM, .....pasi.mustalahtiKILLspam@spam@utu.fi, ptmustaKILLspamutu.fi, http://www.utu.fi/~ptmusta Lab.ins. (mikrotuki) ATK-keskus/Mat.Luon.Tdk OH1HEK Lab.engineer (PC support) Computer Center OI7234 Mail: Turun Yliopisto / Fysla, Vesilinnantie 5, 20014 Pt 02-3336669, FAX 02-3335632 (Pk 02-2387010, NMT 049-555577) --------------------------------------------------------------------------