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例7. OWWriteByte程序

1-Wire读字节命令(96h)从1-Wire网络读取单个数据字节。在DS2482执行该命令之前，必须等1-Wire的工作状态结束。图10所示为I²C通信流程，1-Wire读字节命令程序如例8。发送读字节命令之前，必须检查1-Wire的工作状态是否结束。


图10. 1-Wire读字节。从1-Wire总线上读取一个字节。连续检测状态寄存器直到1WB位从1变为0。然后设置读指针指向读数据寄存器(代码E1h)，并再次访问该器件，读取从1-Wire总线上得到的数据字节。

//-------------------------------------------------------------------------- // Send 8 bits of read communication to the 1-Wire Net and return the // result 8 bits read from the 1-Wire Net. // // Returns: 8 bits read from 1-Wire Net // unsigned char OWReadByte(void) { unsigned char data, status; int poll_count = 0; // 1-Wire Read Bytes (Case C) // S AD,0 [A] 1WRB [A] Sr AD,1 [A] [Status] A [Status] A\ // \--------/ // Repeat until 1WB bit has changed to 0 // Sr AD,0 [A] SRP [A] E1 [A] Sr AD,1 [A] DD A\ P // // [] indicates from slave // DD data read I2C_start(); I2C_write(I2C_address | I2C_WRITE, EXPECT_ACK); I2C_write(CMD_1WRB, EXPECT_ACK); I2C_rep_start(); I2C_write(I2C_address | I2C_READ, EXPECT_ACK); // loop checking 1WB bit for completion of 1-Wire operation // abort if poll limit reached status = I2C_read(ACK); do { status = I2C_read(status & STATUS_1WB); } while ((status & STATUS_1WB) && (poll_count++ < POLL_LIMIT)); // check for failure due to poll limit reached if (poll_count >= POLL_LIMIT) { // handle error // ... DS2482_reset(); return 0; } I2C_rep_start(); I2C_write(I2C_address | I2C_WRITE, EXPECT_ACK); I2C_write(CMD_SRP, EXPECT_ACK); I2C_write(0xE1, EXPECT_ACK); I2C_rep_start(); I2C_write(I2C_address | I2C_READ, EXPECT_ACK); data = I2C_read(NACK); I2C_stop(); return data; }

例8. OWReadByte程序

OWBlock用于执行一组1-Wire字节操作，对于1-Wire网络的数据块传输非常有用。例9所示为OWBlock例程。

//-------------------------------------------------------------------------- // The 'OWBlock' transfers a block of data to and from the // 1-Wire Net. The result is returned in the same buffer. // // 'tran_buf' - pointer to a block of unsigned // chars of length 'tran_len' that will be sent // to the 1-Wire Net // 'tran_len' - length in bytes to transfer // void OWBlock(unsigned char *tran_buf, int tran_len) { int i; for (i = 0; i < tran_len; i++) tran_buf[i] = OWTouchByte(tran_buf[i]); } //-------------------------------------------------------------------------- // Send 8 bits of communication to the 1-Wire Net and return the // result 8 bits read from the 1-Wire Net. The parameter 'sendbyte' // least significant 8 bits are used and the least significant 8 bits // of the result are the return byte. // // 'sendbyte' - 8 bits to send (least significant byte) // // Returns: 8 bits read from sendbyte // unsigned char OWTouchByte(unsigned char sendbyte) { if (sendbyte == 0xFF) return OWReadByte(); else

{ OWWriteByte(sendbyte); return sendbyte; } }

例9. OWBlock程序

1-Wire搜索命令用于搜索1-Wire网络中每个器件唯一的64位注册码，这个唯一的注册码通常在数据资料中用ROM码表示，因为它存储在只读存储器。搜索从1-Wire复位开始，随后是搜索命令。所有1-Wire器件应答的搜索命令是F0h。搜索命令之后，1-Wire主机将进行二叉树搜索，找到一个器件。二叉树搜索通过以下操作判断64位的每一位：首先读一位，读取该位的补码，然后写入一位以确定留在搜索中的器件。这三个单独的位操作时序称为三合一操作。DS2482带有一个简短命令，利用该三合一命令可以更高效地执行1-Wire搜索。

三合一命令(78h)可在1-Wire总线上产生3个时隙，其中包括两个读时隙和一个写时隙。状态寄存器中的方向字节(DIR)决定了写时隙的类型(图11)。例10介绍了完整的1-Wire搜索过程，采用1-Wire三合一命令。调用OWFirst，然后重复调用OWNext，可以查找到1-Wire网络的所有器件。有关1-Wire搜索算法的详细介绍请参考应用笔记187，“1-Wire搜索算法”。


图11. 1-Wire三合一命令，在1-Wire总线上实现搜索ROM功能。完成该1-Wire功能需要空闲时间。然后在读模式下访问器件，通过1-Wire三合一命令得到结果。

// Search state unsigned char ROM_NO[8]; int LastDiscrepancy; int LastFamilyDiscrepancy; int LastDeviceFlag; unsigned char crc8; //-------------------------------------------------------------------------- // Find the 'first' devices on the 1-Wire network // Return TRUE : device found, ROM number in ROM_NO buffer // FALSE : no device present // int OWFirst() { // reset the search state LastDiscrepancy = 0; LastDeviceFlag = FALSE; LastFamilyDiscrepancy = 0; return OWSearch(); } //-------------------------------------------------------------------------- // Find the 'next' devices on the 1-Wire network // Return TRUE : device found, ROM number in ROM_NO buffer // FALSE : device not found, end of search // int OWNext() { // leave the search state alone return OWSearch(); } //-------------------------------------------------------------------------- // The 'OWSearch' function does a general search. This function // continues from the previous search state. The search state // can be reset by using the 'OWFirst' function. // This function contains one parameter 'alarm_only'. // When 'alarm_only' is TRUE (1) the find alarm command // 0xEC is sent instead of the normal search command 0xF0. // Using the find alarm command 0xEC will limit the search to only // 1-Wire devices that are in an 'alarm' state. // // Returns: TRUE (1) : when a 1-Wire device was found and its // Serial Number placed in the global ROM // FALSE (0): when no new device was found. Either the // last search was the last device or there // are no devices on the 1-Wire Net. // int OWSearch() { int id_bit_number; int last_zero, rom_byte_number, search_result; int id_bit, cmp_id_bit; unsigned char rom_byte_mask, search_direction, status; // initialize for search id_bit_number = 1; last_zero = 0; rom_byte_number = 0; rom_byte_mask = 1; search_result = FALSE; crc8 = 0; // if the last call was not the last one if (!LastDeviceFlag) { // 1-Wire reset if (!OWReset()) { // reset the search LastDiscrepancy = 0; LastDeviceFlag = FALSE; LastFamilyDiscrepancy = 0; return FALSE; } // issue the search command OWWriteByte(0xF0); // loop to do the search do { // if this discrepancy if before the Last Discrepancy // on a previous next then pick the same as last time if (id_bit_number < LastDiscrepancy) { if ((ROM_NO[rom_byte_number] & rom_byte_mask) > 0) search_direction = 1; else search_direction = 0; } else { // if equal to last pick 1, if not then pick 0 if (id_bit_number == LastDiscrepancy) search_direction = 1; else search_direction = 0; } // Perform a triple operation on the DS2482 which will perform // 2 read bits and 1 write bit status = DS2482_search_triplet(search_direction); // check bit results in status byte id_bit = ((status & STATUS_SBR) == STATUS_SBR); cmp_id_bit = ((status & STATUS_TSB) == STATUS_TSB); search_direction = ((status & STATUS_DIR) == STATUS_DIR) ? (byte)1 : (byte)0; // check for no devices on 1-Wire if ((id_bit) && (cmp_id_bit)) break; else { if ((!id_bit) && (!cmp_id_bit) && (search_direction == 0)) { last_zero = id_bit_number; // check for Last discrepancy in family if (last_zero < 9) LastFamilyDiscrepancy = last_zero; } // set or clear the bit in the ROM byte rom_byte_number // with mask rom_byte_mask if (search_direction == 1) ROM_NO[rom_byte_number] |= rom_byte_mask; else ROM_NO[rom_byte_number] &= (byte)~rom_byte_mask; // increment the byte counter id_bit_number // and shift the mask rom_byte_mask id_bit_number++; rom_byte_mask <<= 1; // if the mask is 0 then go to new SerialNum byte rom_byte_number // and reset mask if (rom_byte_mask == 0) { calc_crc8(ROM_NO[rom_byte_number]); // accumulate the CRC rom_byte_number++; rom_byte_mask = 1; } } } while(rom_byte_number < 8); // loop until through all ROM bytes 0-7 // if the search was successful then if (!((id_bit_number < 65) || (crc8 != 0))) { // search successful so set LastDiscrepancy,LastDeviceFlag // search_result LastDiscrepancy = last_zero; // check for last device if (LastDiscrepancy == 0) LastDeviceFlag = TRUE; search_result = TRUE; } } // if no device found then reset counters so next // 'search' will be like a first if (!search_result || (ROM_NO[0] == 0)) { LastDiscrepancy = 0; LastDeviceFlag = FALSE; LastFamilyDiscrepancy = 0; search_result = FALSE; } return search_result; } //-------------------------------------------------------------------------- // Use the DS2482 help command '1-Wire triplet' to perform one bit of a //1-Wire search. //This command does two read bits and one write bit. The write bit // is either the default direction (all device have same bit) or in case of // a discrepancy, the 'search_direction' parameter is used. // // Returns – The DS2482 status byte result from the triplet command // unsigned char DS2482_search_triplet(int search_direction) { unsigned char status; int poll_count = 0; // 1-Wire Triplet (Case B) // S AD,0 [A] 1WT [A] SS [A] Sr AD,1 [A] [Status] A [Status] A\ P // \--------/ // Repeat until 1WB bit has changed to 0 // [] indicates from slave // SS indicates byte containing search direction bit value in msbit I2C_start(); I2C_write(I2C_address | I2C_WRITE, EXPECT_ACK); I2C_write(CMD_1WT, EXPECT_ACK); I2C_write(search_direction ? 0x80 : 0x00, EXPECT_ACK); I2C_rep_start(); I2C_write(I2C_address | I2C_READ, EXPECT_ACK); // loop checking 1WB bit for completion of 1-Wire operation // abort if poll limit reached status = I2C_read(ACK); do { status = I2C_read(status & STATUS_1WB); } while ((status & STATUS_1WB) && (poll_count++ < POLL_LIMIT)); I2C_stop(); // check for failure due to poll limit reached if (poll_count >= POLL_LIMIT) { // handle error // ... DS2482_reset(); return 0; } // return status byte return status; }

例10. OWSearch程序

例11给出了如何用DS2482改变1-Wire总线速率的例程，所有1-Wire器件默认工作在标准通信速率，有些器件可以通过Overdrive-Match-ROM或Overdrive-Skip-ROM命令转移到高速工作模式。一旦器件工作在高速模式，所有1-Wire通信将采用高速时序。标准速率的1-Wire复位命令将使所有器件恢复到标准速率。

//-------------------------------------------------------------------------- // Set the 1-Wire Net communication speed. // // 'new_speed' - new speed defined as // MODE_STANDARD 0x00 // MODE_OVERDRIVE 0x01 // // Returns: current 1-Wire Net speed // int OWSpeed(int new_speed) { // set the speed if (new_speed == MODE_OVERDRIVE) c1WS = CONFIG_1WS; else c1WS = FALSE; // write the new config DS2482_write_config(c1WS | cSPU | cPPM | cAPU); return new_speed; }

例11. OWSpeed程序

例12给出了如何用DS2482改变1-Wire总线电平的程序，DS2482可以在执行一次位或字节通信后使能强上拉。随后，OWLevel程序将1-Wire网络返回到标准上拉，利用OWWriteBytePower或OWReadBitPower操作使能强上拉。

//-------------------------------------------------------------------------- // Set the 1-Wire Net line level pullup to normal. The DS2482 only // allows enabling strong pullup on a bit or byte event. Consequently this // function only allows the MODE_STANDARD argument. To enable strong pullup // use OWWriteBytePower or OWReadBitPower. // // 'new_level' - new level defined as // MODE_STANDARD 0x00 // // Returns: current 1-Wire Net level // int OWLevel(int new_level) { // function only will turn back to non-strong pullup if (new_level != MODE_STANDARD) return MODE_STRONG; // clear the strong pullup bit in the global config state cSPU = FALSE; // write the new config DS2482_write_config(c1WS | cSPU | cPPM | cAPU); return MODE_STANDARD; }

例12. OWLevel程序

例13是OWReadBitPower所使用的程序，用于读取一个1-Wire位并执行供电功能。当配置寄存器中的强上拉(SPU)位使能时，在下一位或字节通信完成后，DS2482将有源拉高1-Wire总线。该操作可通过是否获得相应的响应来验证读位的正确性，如果响应不正确，1-Wire电平将返回到标准的上拉状态。

//-------------------------------------------------------------------------- // Send 1 bit of communication to the 1-Wire Net and verify that the // response matches the 'applyPowerResponse' bit and apply power delivery // to the 1-Wire net. Note that some implementations may apply the power // first and then turn it off if the response is incorrect. // // 'applyPowerResponse' - 1 bit response to check, if correct then start // power delivery // // Returns: TRUE: bit written and response correct, strong pullup now on // FALSE: response incorrect // int OWReadBitPower(int applyPowerResponse) { unsigned char rdbit; // set strong pullup enable cSPU = CONFIG_SPU; // write the new config if (!DS2482_write_config(c1WS | cSPU | cPPM | cAPU)) return FALSE; // perform read bit rdbit = OWReadBit(); // check if response was correct, if not then turn off strong pullup if (rdbit != applyPowerResponse) { OWLevel(MODE_STANDARD); return FALSE; } return TRUE; }

例13. OWReadBitPower程序

例14为OWWriteBytePower所采用的程序，用于写入1-Wire字节并执行强上拉供电功能。当配置寄存器中的强上拉(SPU)位使能时，在下一位或字节通信完成后，DS2482将由源拉高1-Wire总线。

//-------------------------------------------------------------------------- // Send 8 bits of communication to the 1-Wire Net and verify that the // 8 bits read from the 1-Wire Net are the same (write operation). // The parameter 'sendbyte' least significant 8 bits are used. After the // 8 bits are sent change the level of the 1-Wire net. // // 'sendbyte' - 8 bits to send (least significant bit) // // Returns: TRUE: bytes written and echo was the same, strong pullup now on // FALSE: echo was not the same // int OWWriteBytePower(int sendbyte) { // set strong pullup enable cSPU = CONFIG_SPU; // write the new config if (!DS2482_write_config(c1WS | cSPU | cPPM | cAPU)) return FALSE; // perform write byte OWWriteByte(sendbyte); return TRUE; }

例14. OWWriteBytePower程序

DS2482已经过测试，可成功完成I²C接口至1-Wire网络的转换。本文给出了基于DS2482 I²C 1-Wire线驱动器的完整的1-Wire接口方案，该接口适用于所有1-Wire器件，所提供的例程可以在任何一个具有I²C通信口的主机上轻松实现。另外还提供可供下载的完整的C语言执行程序。测试平台是CMAXQUSB评估套件。

修订历史
11/2005版本1.0–首次发布。
9/2008版本2.0–修改程序以使用低电平I²C通信子程序，修改相应的文字内容。