lcd_i2c.cpp

00001 #include "mbed.h"
00002 #include "lcd_i2c.h"
00003 /*
00004     LCD (Optrex DCM16230, DCM20261, etc.)  via I2C using a PCF8574
00005 
00006                                   Frequency (clks/sec)                    Frequency
00007     Transfer rate = ------------------------------------------------ = ---------------- (characters/sec)
00008                 9 clks/write * 3 writes/nibble * 2 nibbles/character      54
00009 */
00010 I2C i2c(p9, p10);           // (sda, scl)
00011 Serial pc2(USBTX, USBRX);    // tx, rx
00012 
00013 // PCF8574 output bits     Px
00014 #define     RS      BIT1
00015 #define     RW      BIT2
00016 #define     E       BIT3
00017 #define     DB4     BIT4
00018 #define     DB5     BIT5
00019 #define     DB6     BIT6
00020 #define     DB7     BIT7
00021 
00022 char update[NUPDATE];
00023 char cw, address;
00024 
00025 int updateDisplay(char *str, int nchars)
00026 {
00027 char w, ch, *p;
00028 int n, k, rc;
00029 
00030     if (nchars > 20)
00031         return 1;
00032     n = 0;
00033     p = update;
00034     for (k = 0; k < nchars; k++)
00035     {
00036         // write most significant nibble
00037         ch = *str++;
00038         w = (ch & 0xf0) | cw;
00039         *p++ = w;
00040         *p++ = w | E;
00041         *p++ = w;
00042 
00043         // write least significant nibble
00044         w = (ch << 4) | cw;
00045         *p++ = w;
00046         *p++ = w | E;
00047         *p++ = w;
00048         n += 6;
00049     }
00050     rc = i2c.write(address, update, n);  // rc == 0 ==> ACK
00051     return rc;
00052 }
00053 
00054 int write4Bits(char data)
00055 {
00056 char w;
00057 int rc;
00058 
00059     w = (data & 0xf0) | cw;     // grab the left nibble
00060     update[0] = w;
00061     update[1] = w | E;
00062     update[2] = w & ~ E;
00063     rc = i2c.write(address, update, 3);
00064     return rc;
00065 }
00066 
00067 int initLcd(int i2cAddress, int frequency)
00068 {
00069 typedef struct {
00070     char    cmd;
00071     char    numNibbles;
00072     char    delayMs;
00073     //char  testBF;
00074 } INIT;
00075 static const INIT initData[] = {
00076     {3, 1, 5},
00077     {3, 1, 1},
00078     {3, 1, 1},
00079     {2, 1, 1},      // Function set: 4-bit interface
00080     {0x28, 2, 2},   // Function set: 2 lines, 5x7
00081     {0x08, 2, 2},   // Display off
00082     {0x01, 2, 16},  // Clear display
00083     {0x06, 2, 2},   // Entry mode set: No increment, shift cursor
00084     {0x0e, 2, 2}};  // Display on: cursor on, blink off
00085 #define NINITD (sizeof(initData)/sizeof(initData[0]))
00086 INIT *p;
00087 int k, rc;
00088     // Initialization must start at least 16 ms after power up.
00089     i2c.frequency(frequency);
00090     address = i2cAddress;
00091     cw = 0;
00092     p = (INIT *)initData;
00093     for (k = 0; k < NINITD; k++)
00094     {
00095         //p = (INIT *)&initData[k];
00096         if (p->numNibbles == 1)
00097             rc = write4Bits(p->cmd << 4);
00098         else
00099         {
00100             rc = write4Bits(p->cmd);        // output the most significant nibble
00101             wait_us(10);                    // this will need to be adjusted when printf stmts are removed
00102             rc |= write4Bits(p->cmd << 4);  // output the least significant nibble
00103         }
00104         if (rc)
00105             break;
00106         wait_ms(p->delayMs);
00107         p++;
00108     }
00109     return rc;
00110 }
00111 
00112 int lcdWriteMsg(char *msg)
00113 {   // msg must be a null-terminated string
00114 char rc;
00115     cw |= RS;       // data
00116     cw &= ~RW;      // write
00117     rc = updateDisplay(msg, strlen(msg));
00118     return rc;
00119 }
00120 
00121 int lcdWriteCmd(char cmd, int delayMs)
00122 {
00123 int rc;
00124     cw &= ~RS;      // command
00125     rc = write4Bits(cmd);
00126     wait_us(10);
00127     rc |= write4Bits(cmd << 4);
00128     if (delayMs)
00129         wait_ms(delayMs);
00130     return rc;
00131 }
00132 
00133 int lcdPositionCursor(char row, char col)
00134 {
00135 // Code may not be correct for displays larger than 20 x 2
00136 int x, rc;
00137     x = 0x80 | ((row & 1)<<6) | (col & 0xf);
00138     rc = lcdWriteCmd(x, 1);
00139     return rc;
00140 }
00141 
00142 int lcdClearDisplay(void)
00143 {
00144     return lcdWriteCmd(1, 16);
00145 }
00146 
00147 
00148