74hc164 Schematic & Sample Code

everest · 2009-08-30 16:05

Hello,

I need to free up some pins from my Stamp2 application. After doing some digging and research it appears that the simplest way to do this is via a 74hc164 for inputs and a 74HC595 for outputs. I dug and for the life of me I can't seem to find a simple example of how to build a circuit along with sample code. I just know there is a Nuts & Volts article out there waiting that covers this. . .I found one, but it looks like they are using a totally separate PIC microcontroller and I'd like to avoid that if I can.

Any suggestions/pointers?

-JEff

PJAllen · 2009-08-30 21:13

For inputs, it's a 74HC165.· For outputs, it's a 74HC595.··StampWorks (<-- hot-link!) has the information you require.

dev/null · 2009-08-30 21:37

74HC595

Schematics (with 8 LED's connected):

Code:

' {$STAMP BS2p}
' {$PBASIC 2.5}

  pHCIO         CON     0                        ' 74HC595 data
  pHCCLK        CON     1                        ' 74HC595 clock
  pHCLtc        CON     2                        ' 74HC595 latch

Main:
  HCBits = %01000100
  GOSUB WriteHC
  END

WriteHC:
  SHIFTOUT pHCIO, pHCCLK, MSBFIRST, [noparse][[/noparse]HCBits]
  PULSOUT pHCLtc, 1
  PAUSE 50
  RETURN

74HC165

Schematics (with 8 switches):

Code:

' {$STAMP BS2p}
' {$PBASIC 2.5}
' This program demonstrates a simple method of turning three BASIC Stamp
' I/O pins into eight digital inputs with a 74HC165 shift register.

' -----[noparse][[/noparse] I/O Definitions ]-------------------------------------------------
Clock PIN 0 ' shift clock (74HC165.2)
SerData PIN 1 ' serial data (74HC165.7)
Load PIN 2 ' output latch (74HC165.1)

' -----[noparse][[/noparse] Constants ]-------------------------------------------------------
DelayTime CON 100

' -----[noparse][[/noparse] Variables ]-------------------------------------------------------
switches VAR Byte ' switch data

' -----[noparse][[/noparse] Initialization ]--------------------------------------------------
Reset:
    HIGH Load ' make output and high
    DEBUG CLS,
    "Switches 76543210", CR,
    "-------- --------", CR,
    "Status ........"

' -----[noparse][[/noparse] Program Code ]----------------------------------------------------
Main:
    DO
        GOSUB Get_165 ' get switch inputs
        DEBUG CRSRXY, 10, 2, BIN8 switches ' display current status
        PAUSE DelayTime ' pad the loop a bit
    LOOP

' -----[noparse][[/noparse] Subroutines ]-----------------------------------------------------
Get_165:
    PULSOUT Load, 5 ' load switch inputs
    SHIFTIN SerData, Clock, MSBPRE, [noparse][[/noparse]switches] ' shift them in

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Don't worry. Be happy

dev/null · 2009-08-30 22:05

Correction:

' {$STAMP BS2p}
' {$PBASIC 2.5}

  pHCIO         CON     0                        ' 74HC595 data
  pHCCLK        CON     1                        ' 74HC595 clock
  pHCLtc        CON     2                        ' 74HC595 latch
  HCBits     VAR Byte

Main:
  HCBits = %01000100
  GOSUB WriteHC
  END

WriteHC:
  SHIFTOUT pHCIO, pHCCLK, MSBFIRST, [noparse][[/noparse]HCBits]
  PULSOUT pHCLtc, 1
  PAUSE 50
  RETURN

Also, forgot RETURN statement in the 165 code snippet.

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Don't worry. Be happy

everest · 2009-08-31 01:13

Thanks! I found some excellent links that show exactly how this is done. . .looks very straightforward!!

I do still have one remaining question though. . .is it possible to read the current position of the outputs controlled by the 75HC595? The examples provided and the ones I found show how to write and change the state, but not necessarily how to read the state of all the switches. I really need to be able to do both. . .

-Jeff

Post Edited (everest) : 8/31/2009 1:18:24 AM GMT

dev/null · 2009-08-31 07:44

No you can't read the switches of a 74HC595. I don't know why you would? You should keep that information in a variable in your Stamp...

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Don't worry. Be happy

dev/null · 2009-08-31 07:45

If you REALLY need to do that, you could connect a 74HC165 to the 74HC595 and read the switches that way.

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Don't worry. Be happy

dev/null · 2009-08-31 08:36

All the outputs of the 74HC595 will be LOW at startup, there is no preserved state in the chip, so whenever you send data to it, you will have that info in your Stamp.

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everest · 2009-08-31 12:35

Ugh. . .okay. That's just going to make the program a bit more complex. I also really need to determine if pin states are reset when I use the "RUN" command to switch program slots. I'm guessing they aren't since that would be a real pain, but I'm away from my Stamps now, so I can't test it. There's going to be a LOT that I'll need to keep track of, so I'm thinking I'll just use Scratch RAM.

-Jeff

dev/null · 2009-08-31 12:48

You can use EEPROM or ScratchPad RAM, your choice. The pins are not reset when you switch program slots. The only time pins are reset is when the power to the 74HC chip is recycled, or you apply a LOW signal to the Reset pin. It's quite easy to use. You keep track of all 8 outputs in a Byte variable, how hard can it be?

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Don't worry. Be happy

dev/null · 2009-08-31 12:58

BTW: If you put your state byte in EEPROM you could preserve state when power is recycled.

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Don't worry. Be happy

kleekru · 2009-09-03 06:05

I need to get back to basics on this post if possible... (I'm still in the "What's a Microcontroller" phase of my learning)...

How would I write Activity #3 from Chapter#3 using· the 74HC165?· Here is the input from the book:

' {$STAMP BS2}
' {$PBASIC 2.5}
' Whats a Microcontroller - CH3ACT3PushbuttoncontrolledLED.bst
' Check· pushbutton state 10 times per second and blink LED when pressed.
DO
· DEBUG ? IN3
· IF (IN3 = 1) THEN
··· HIGH 14
··· PAUSE 50
··· LOW 14
··· PAUSE 50
· ELSE
··· PAUSE 100
· ENDIF
LOOP

I have the·attached schematic wired up with my BS2... but frankly I don't know what my input labels will be (IN3 above will be what now that I have· an input going through the 74HC165 chip???).· Am I thinking about this the wrong way?·

Any advice out there?· Please be specific... and dumb it down for me a bit.

Thanks!
Kevin

74hc164 Schematic & Sample Code

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