Matrix keyboard with State Machine

This is a Stamp Basic code by Tracey Allen to read a 4x4 matrix keyboard with Finite State Machine technique.

I am trying to use this code in PBP but cannot understand how few commands work:

keyn var key0.nib0 ' address the first detection as nibble array

The above seems to alias variable keyn to key0 lowest nibble (this key0 is a word variable). Is that right?

Then, keyn(ix)=kin ' read the row inputs into nibbles of key0

seems to put in an array controlled by ix four values. Though the keyn was not defined as array. How does this work?

Code:

---

' KEY_FSM.BS2
' Tracy Allen, http://www.emesystems.com
' scans a 16 key (4x4) matrix keypad
' using state machine for debouncing, all keys in parallel
' The columns are connected to BS2 outputs of port C, P8 to P11
' The rows are connected to BS2 inputs of port D, P12 to P15
' with pull-up resistors to Vdd=+5 volts.
' This routine has two output variables, "keys" and "keyx"
' Bits in "keys" go low after the corresponding key is
' pressed and debounced.
' Bits in "keyx" go high for _one iteration only_ to signal
' a high to low transition (button pushed & debounced)
' of the corresponding key
' In all state variables, each bit corresponds to one key.
' One word is used for 16 keys, in a 4x4 array.
' This uses a lot of variables, but in many applications it is
' possible to reuse most of the variables outside the keyscan loop
' Note that the scan can detect key combinations.
' The decoding step can miss keys only if they are pressed at
' exactly the same instant.
 
 
 
kout var outC ' 4-bit keypad columns, state, if output
kdir var dirC ' 4-bit keypad columns, input or output
kin var inD ' inputs from keypad rows connected to port D
 ' bit low for key pressed
key0 var word ' state variable, first detection
key1 var word ' state variable, second detection
key2 var word ' state variable, third detection
keyn var key0.nib0 ' address the first detection as nibble array
keys var word ' debounced output, bit low for key pressed
keyz var word ' state variable, previous state of keys
keyx var word ' transition output, bit high one iteration for each press
ix var word ' index for array addressing
 
dirs=%0000111111111111 ' port D is input, all others output
outs=%0000000000000000 ' start with port C columns output low
 ' pins P0 to P7 are not used in this program
debug cls ' Clear screen
 
scanloop:
 key2=key1 ' move the debounced states
 key1=key0
 for ix=0 to 3 ' scan 4 cols by bringing one col at a time low.
 kdir = dcd ix ' 0001,0010,0100,1000 in succession
 ' this makes one column at a time output low
 ' while the other columns are inputs
 keyn(ix)=kin ' read the row inputs into nibbles of key0
 next
 kdir = %1111 ' make all columns output (avoid floating inputs)
 keys=key0&key1&key2|keys ' key bit 0->1 when all 3 are high
 keys=key0|key1|key2&keys ' key bit 1->0 when all 3 are low
 keyx=keys^keyz & keyz ' detect change 1->0 (active low keypress)
 keyz=keys
 ' optional debug to visualize operation of the state machine
 ' slows down the operation tremendously
 ' debug home,bin16 key0,cr,bin16 key1,cr,bin16 key2,cr
 ' debug bin16 keys,32,bin16 keyx,home
 ' optional branch to decode keypress, note keyx is transient
 if keyx>0 then decode
 ' pause 30 ' optional delay to slow the scanning
goto scanloop
 
 
decode:
 code1 var byte ' code1 variable
 code1 = ncd keyx-1 ' binary encode the most significant key
 lookup code1,[10,7,4,1,0,8,5,2,11,9,6,3],code1 ' translate to code
 dtmfout 7,[code1] ' send as touchtone
 lookup code1,["0123456789*#"],code1 ' --> printable character
 debug code1 ' print on screen
goto scanloop

---

Thanks,
Ioannis

"dirs=00111111111111 ' port D is input, all others output"
This looks like PICAXE code.

since pbp has no nibble var type i would guess that

keyn(ix)=kin ' read the row inputs into nibbles of key0

becomes
keyn = keyn & ~$0f<<(ix*4);clear nibble
keyn = keyn | kin<<(ix*4);load new value for nibble

where kin is now a word and

kin var inD
becomes
kin = portd & $f



there is probably better pbp code for reading a keypad floating around

Mike, this is Stamp Basic dialect.

Richard, thanks. This makes more sense now. Yes maybe there is better code for matrix keyboard. I was interested in this because of the debouncing and scanning all at the same time.

Ioannis

See the code examples from Les Johnson in second post. I had this book many years ago, now out of print. You can find pdf's copies on google

http://www.picbasic.co.uk/forum/showthread.php?t=21115

If you're able to understand arduino C, look at the arduino matrix keyboard example. Nice FSM implementation https://domoticx.com/arduino-library-keypad/

Thanks to all!

Ioannis

I did this a long time ago with a 4X4 membrane switch to play messages on an ISD chip.

Low PORTC.7
Pause 1
IF PORTB.4 = 0 Then MESSAGE1
IF PORTB.2 = 0 Then MESSAGE9
High PORTC.7

Low PORTC.6
Pause 1
IF PORTB.4 = 0 Then MESSAGE2
IF PORTB.2 = 0 Then MESSAGE10
High PORTC.6

Low PORTC.2
Pause 1
IF PORTB.4 = 0 Then MESSAGE3
IF PORTB.2 = 0 Then MESSAGE11
High PORTC.2

Low PORTC.1
Pause 1
IF PORTB.4 = 0 Then MESSAGE4
IF PORTB.2 = 0 Then MESSAGE12
High PORTC.1

Low PORTC.0
Pause 1
IF PORTB.4 = 0 Then MESSAGE5
IF PORTB.2 = 0 Then MESSAGE13
High PORTC.0

Low PORTA.0
Pause 1
IF PORTB.4 = 0 Then MESSAGE6
IF PORTB.2 = 0 Then MESSAGE14
High PORTA.0

Low PORTA.1
Pause 1
IF PORTB.4 = 0 Then MESSAGE7
IF PORTB.2 = 0 Then MESSAGE15
High PORTA.1

Low PORTC.4
Pause 1
IF PORTB.4 = 0 Then MESSAGE8
IF PORTB.2 = 0 Then MESSAGE16
High PORTC.4