' KeyPad_RP2040_74HC595_v03.bas - Program for more than 4x4 Key Pad
' Rows scanned by a 74HC595 serial-to-parallel chip
' rows = number of rows. For more than 8 rows daisychain another 74HC595 chip.
' cols =  number of columns
' RowPinGP = row GP pin number for the 74HC595
' ColPinGP = first of the column GP pin numbers
' Key = number of the key that has been pressed.
' eg. 0 to 63 for 8 columns x 8 rows. 1st row 0 to 7, last row 55 to 63.
' X x Y Keypad with buttons bridging column x to row y

Option base 0
Dim integer n, Key=-1, RowPinGP=0, Rows=8, ColPinGP=1, Cols=8
' Dim KeyMap$(rows * cols - 1)=("Q","W","E","R","T","Y", etc) 'map keys to characters with KeyMap$(Key) if req.

Dim integer RowPinNo = MM.Info(pinno "GP"+Str$(RowPinGP))

SetPin RowPinNo, DOUT 'set the output pin to the 74HC595 and set its outputs to 0
HC595 RowPinNo, Rows+7, 0 'Call Sub with DataPin, max. number of Rows, Word to send, 0=all low
'Rows+7 to ensure any unused pins are also set to 0

For n=ColPinGP To ColPinGP+Cols-1
 SetPin MM.Info(pinno "GP"+Str$(n)), INTL, Key.Pad, PULLUP 'set the input Port pins and ISR
Next

Do
' Your main processing loop
If Key+1 Then Print "Key";Key, "&H";Hex$(Key,2), Timer-t;"mS" : key=-1
'to retain the value of Key set a flag in the sub and reset it here
Loop

Sub Key.Pad
 t=Timer
 Local integer y, x, x1, n
 Pause 10 'contact bounce delay, set to minimum value that is reliable

 For y = 0 To rows 'scan the rows
   HC595 RowPinNo, Rows, 1<<y Xor (1<<Rows+1)-1 'Call Sub with DataPin, no. of Rows, Row to read, inverted
   Execute "x1 = (1<<cols)-1 XOR Port(GP"+Str$(ColPinGP)+",cols)" 'read the columns

   If x1 Then x=Log(x1)/Log(2)+1

   If x>cols Or y>rows Then 'check for values out of range and abort this read
     x=0 :y=0 : Key=-1
     HC595 RowPinNo, Rows+7, 0 'prepare for next key input, 0=all low
     Exit Sub
   EndIf
   Key = y * cols + x - 1 'get key no. from row no. and col. no., starting from 0
   If x1 Then Exit For
 Next

 HC595 RowPinNo, Rows+1, (1 << Rows+1)-1 'all high, block further input to prevent double press
 Pause 150 'set to minimum value that is reliable, or remove it and/or the HC595 Sub call above
 HC595 RowPinNo, Rows+7, 0 'prepare for next key input, 0=all low
 'Set a flag here if main prog. needs it
End Sub

Sub HC595 OutPin As integer, R As integer, Dat As integer 'Data output Pin, number of Rows, Word to output
 Pin(OutPin)=1 'ensure correct polarity for Bitstream
 Local integer n, el=R*2-1, B(el)
 For n=0 To el Step 2 'prepare Bitstream array
   B(n)=3-(Dat>>(el-n)\2 And 1)*2 'low data pulses, 3uS=0 ,1uS=1
   B(n+1)=1 '1uS high spaces
 Next
 Device BITSTREAM OutPin, R*2, B() 'send it
 Pin(OutPin)=1 : Pause 0.04 ' >20uS high = latch clock
End Sub
End
'  74HC595 connections
' 3V3 to pins 16, 10
' Gnd to pins 8, 13
' BitStream input to pin 11 (clock)
' pin 11 - 1k8 - pin 14 (data in) - 1n5 - Gnd
' pin 11 - A-diode-K - pin 14 (ser. data in) eg 1N914 or 1N4148
' pin 11 - 4k7 - pin 12 (latch) - 1n5 - Gnd
' pin 11 - K-diode-A - pin 14 (latch)
' pin 9 (ser. data out) to next 74HC595 (if used) pin 14 (ser. data in),
' parallel pin 11 to pin 11 and pin 12 to pin 12
' Row output pins:- 15, 1, 2, 3, 4, 5, 6, 7

' KeyPad_RP2040_74HC595_2_Pin_v01.bas - Program 4x4 Key Pad
'
' Keypad reader using a 74HC595 and 2 MCU I/O pins.
' For more than 8 rows plus columns daisy-chain another 74HC595 chip or two.
' then adjust the Rows and Cols limits for the For / Next loops.
' 1 chip is up to 16 Keys, 2 is up to 64 (8 x 8), 3 is up to 144 (12 x 12)
' keypad does not need to be square. 2 chips = 16 outputs so could do 12 x 4 (12 + 4 = 16)
'
Dim Integer Rows = 4, Cols = 4, Key = -1, OutPin=MM.Info(pinno GP0), InPin=MM.Info(pinno GP1)
SetPin OutPin,dout : Pin(OutPin)=1 'initialize keypad row output
HC595 OutPin,Rows+Cols,0   'set all pins low
SetPin InPin,intl,KP_int,pullup 'initialize keypad column input

Sub KP_Int
  Pause 2 'key de-bounce time, adjust to suit your keypad
  Local integer R, C

  For R=0 To Rows-1   'Scan the rows (low) one at a time, the rest high
   HC595 OutPin,Rows+Cols,15-(1<<R)
   If 1-Pin(InPin) Then Exit For 'exit when the active row is found
  Next

  For C=0 To Cols-1   'Scan the columns (low) one at a time, the rest high
   HC595 1,Rows+Cols, (15-(1<<C))<<4
   If 1-Pin(InPin) Then Exit For 'exit when the active column is found
  Next

  If Rows-R Then Key = R*Rows+C 'Evaluate the key unless the row count is too high
  'Set a flag here if the main loop needs it.
  HC595 OutPin,Rows+Cols,0 'Prepare for next press, set all pins low
End Sub

Sub HC595 Out.Pin As integer, RC As integer, Dat As integer
  'Data output Pin, number of Rows+Cols, Word to output
  Pin(Out.Pin)=1 'ensure correct polarity for Bitstream
  Local integer n, el=RC*2-1, B(el)
  Array Set 1,B() '1uS low data and 1uS high spaces = all 1s
  For n=0 To el Step 2 'prepare Bitstream array
    B(n)=3-(Dat>>(el-n)\2 And 1)*2 'low data pulses, 0 = 3uS, 1 = 1uS
  Next
  Device BITSTREAM Out.Pin, el+1, B() 'send it
  Pin(Out.Pin)=1 : Pause 0.025 ' >20uS high = latch clock
End Sub

Do
  If Key+1 Then Print "Key";Key : Key = -1
  'If you need to preserve the value of "Key" replace "Key+1" with a flag
  ' that was set in the ISR and reset the flag instead of "Key = -1"
Loop

End
'  74HC595 connections
' 3V3 to pins 16, 10
' Gnd to pins 8, 13
' BitStream input to pin 11 (clock)
' pin 11 - 1k8 - pin 14 (data in) - 1n5 - Gnd
' pin 11 - A-diode-K - pin 14 (ser. data in) eg 1N914 or 1N4148
' pin 11 - 4k7 - pin 12 (latch) - 1n5 - Gnd
' pin 11 - K-diode-A - pin 14 (latch)
' pin 9 (ser. data out) to next 74HC595 (if used) pin 14 (ser. data in),
' parallel pin 11 to pin 11 and pin 12 to pin 12
' 4x4 Row output pins:- 15, 1, 2, 3,
' 4x4 Column output pins:- 4, 5, 6, 7

Key 0    5.003000006 mS
Key 1    4.600000001 mS
Key 2    6.101999998 mS
Key 3    6.671000004 mS
Key 4    4.600999996 mS
Key 5    6.107000001 mS
Key 6    5.691 mS
Key 7    6.275000006 mS
Key 8    5.148000002 mS
Key 9    6.662 mS
Key 10   7.221000001 mS
Key 11   7.800999999 mS
Key 12   6.663000003 mS
Key 13   7.230999999 mS
Key 14   6.831 mS
Key 15   7.395999998 mS

'PCF8574 4x4 keyboard
'connect keyboard rows to pins 9,10,11,12, and columns to pin 4,5,6,7

pcf%=&h20            'I2C address when A0/A1/A2 are GND
pinrow%=&b00001111   'setup rows and columns, lsb in, msb out

'for decoding
Dim pin2num%(15)=(8,8,8,8,8,8,8,3,8,8,8,2,8,1,0,8)
Dim rowpat%(3)=(&b01111111,&b10111111,&b11011111,&b11101111)


'---------------------------- main program -----------------------

'init default for rows and columns
I2C2 write pcf%,0,1,pinrow%


'main loop
Do
 I2C2 read pcf%,0,1,d%                'read keyboard
 If d%<>pinrow% Then                  'check if key pressed
   Print whatkey%()                   'show the key after scanning
 End If

 Pause 100
Loop


'------------------------------- subs -----------------------------

'scan keys
Function whatkey%()
 Local i%,d%
 For i% = 0 To 3                      'scan rows
   I2C2 write pcf%,0,1,rowpat%(i%)    'push pattern
   I2C2 read pcf%,0,1,d%              'read response
   If d%<>rowpat%(i%) Then            'different then key pressed
     whatkey%=i%+4*pin2num%(d% And 15)'decode
     I2C2 write pcf%,0,1,pinrow%      'restore default rows
     Exit Function                    'and quit
   End If
 Next
End Function

  ┌────────────┐                             The keypad that I tested with has an 8-pin header:
  │ 1  2  3  A │─┳──────┐                     1 - row 2    (4,5,6,B)                          
  │            │  30K   │                     2 - row 3    (7,8,9,C)                          
  │ 4  5  6  B │─┫      ⏚                     3 - column 1 (1,4,7,*)                          
  │            │  30K                         4 - row 4    (*,0,#,D)                          
  │ 7  8  9  C │─┫                            5 - column 2 (2,5,8,0)                          
  │            │  30K                         6 - column 3 (3,6,9,#)                          
  │ *  0  #  D │─┫                            7 - column 4 (A,B,C,D)  
  └────────────┘  30K                         8 - row 1    (1,2,3,A)          
              │                                                                            
    ┣┻┻┻────┘                      
     7.5K                                
    ┣─────────────────── I/O pin        
   1000pF