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max7219/README.md

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+# Max7219 7-Segment/Matrix LED Driver
+
+## Introduction
+
+The Maxim 7219 LED driver is an SPI chip that simplifies driving 7-Segment LED 
+displays. It's also commonly used to create 8x8 LED matrixes. The datasheet 
+is available at:
+
+https://www.analog.com/media/en/technical-documentation/data-sheets/MAX7219-MAX7221.pdf
+
+You can find 8 digit, 7-segment LED boards on Ebay for $1-2. You can find 
+inexpensive matrixes in various sizes from 1 - 8 segments as well. 
+
+For matrixes, the driver provides a basic CP437 font that can be used to
+display characters on 8x8 matrixes. If desired, you can supply your own glyph
+set, or special characters for your specific application.
+
+## Driver Functions
+
+This driver provides simplified handling for using either 7-segment numeric 
+displays, or 8x8 matrixes.
+
+It provides methods for scrolling data across either one or multiple displays.
+For example, you can pass an IP address of "10.100.10.11" to the scroll function
+and it will automatically scroll the display a desired number of times. The 
+scroll feature also works with matrixes, and scrolls characters one LED column
+at a time for a smooth, even display.
+
+## Notes About Daisy-Chaining
+
+The Max7219 is specifically designed to handle larger displays by daisy chaining 
+units together. Say you want to write to digit 8 on the 3rd unit chained 
+together. You would make one SPI write. The first write would be the register 
+number (8), and the data value. Next, you would write a NOOP. The first record 
+would then be shifted to the second device. Finally, you write another NOOP. The 
+first record is shifted from the second device to the 3rd device, the first NOOP is 
+shifted to the second device. When the ChipSelect line goes low, each unit applies 
+the last data it received.

max7219/example_test.go

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+// Copyright 2024 The Periph Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package max7219_test
+
+import (
+	"fmt"
+	"log"
+	"time"
+
+	"periph.io/x/conn/v3/driver/driverreg"
+	"periph.io/x/conn/v3/spi/spireg"
+	"periph.io/x/devices/v3/max7219"
+	"periph.io/x/host/v3"
+)
+
+// basic test program. To do a numeric display, set matrix to false and
+// matrixUnits to 1.
+func Example() {
+	var matrix = false
+	matrixUnits := 1
+	var err error
+	_, err = host.Init()
+	if err != nil {
+		log.Fatal(err)
+	}
+	if _, err = driverreg.Init(); err != nil {
+		log.Fatal(err)
+	}
+
+	s, err := spireg.Open("")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer s.Close()
+
+	dev, err := max7219.NewSPI(s, matrixUnits, 8)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	_ = dev.TestDisplay(true)
+	time.Sleep(time.Second * 1)
+	_ = dev.TestDisplay(false)
+
+	_ = dev.SetIntensity(1)
+	_ = dev.Clear()
+
+	if matrix {
+		dev.SetGlyphs(max7219.CP437Glyphs, true)
+		dev.SetDecode(max7219.DecodeNone)
+		dev.ScrollChars([]byte("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"), 1, 100*time.Millisecond)
+	}
+
+	// display a count
+	for i := -128; i < 128; i++ {
+		dev.WriteInt(i)
+		time.Sleep(100 * time.Millisecond)
+	}
+	var tData []byte
+	// Continuously display a clock
+	for {
+		t := time.Now()
+		if matrix {
+			// Assumes a 4 unit matrix
+			tData = []byte(fmt.Sprintf("%2d%02d", t.Hour(), t.Minute()))
+		} else {
+			// 8 digit 7-segment LED display
+			tData = []byte(t.Format(time.TimeOnly))
+			tData[2] = max7219.ClearDigit
+			tData[5] = max7219.ClearDigit
+		}
+		_ = dev.Write(tData)
+		// Try to get the iteration exactly on time. FWIW, on a Pi Zero this loop
+		// executes in ~ 2-3ms.
+		dNext := time.Duration(1000-(t.UnixMilli()%1000)) * time.Millisecond
+		time.Sleep(dNext)
+	}
+}