OWOUT

Syntax: OWOUT Pin, Mode, [OutputData]

Function

Send data to a device using the Maxim/Dallas Semiconductor 1-Wire^®protocol.

• Pin is a variable/constant/expression (0 - 15) that specifies which I/O pin to use. 1-Wire devices require only one I/O pin (called DQ) to communicate. This I/O pin will be toggled between output and input mode during the OWOUT command and will be set to input mode by the end of the OWOUT command.
• Mode is a variable/constant/expression (0 - 15) indicating the mode of data transfer. The Mode argument controls placement of reset pulses (and detection of presence pulses) as well as byte vs. bit input and normal vs. high^† speed. See explanation below.
• OutputData is a list of variables and modifiers that tells OWOUT how to format outgoing data. OWOUT can transmit individual or repeating bytes, convert values into decimal, hexadecimal or binary text representations, or transmit strings of bytes from variable arrays. These actions can be combined in any order in the OutputData list.

Quick Facts

Explanation

The 1-Wire protocol is a form of asynchronous serial communication developed by Maxim/Dallas Semiconductor. It only requires one I/O pin and that pin can be shared between multiple 1-Wire devices. The OWOUT command allows the BASIC Stamp to send data to a 1-Wire device.

The following is an example of the OWOUT command:

   OWOUT 0, 1, [$4E]

This code will transmit a "reset" pulse to a 1-Wire device (connected to I/O pin 0) and then will detect the device's "presence" pulse and then transmit one byte (the value $4E).

The Mode argument is used to control placement of reset pulses (and detection of presence pulses) and to designate byte vs. bit input and normal vs. high speed^†. The tables below show the meaning of each of the four bits of Mode and some of the 16 possible values and their effect.

^† The BS2pe is not capable of High Speed transfers.

The proper value for Mode depends on the 1-Wire device and the portion of the communication you're working on. Please consult the data sheet for the device in question to determine the correct value for Mode. In many cases, however, when using the OWOUT command, Mode should be set for a Front-End Reset (to initialize the transaction). This may vary due to device and application requirements, however.

When using the Bit (rather than Byte) mode of data transfer, all variables in the OutputData argument will only transmit one bit. For example, the following code could be used to send two bits using this mode:

bitOne  VAR     Bit
bitTwo  VAR     Bit

Init:
  bitOne = 0
  bitTwo = 1

Main:
  OWOUT 0, 5, [bitOne, bitTwo]
  STOP

In the code above, we chose the value "5" for Mode. This sets Bit transfer and Front-End Reset modes. Also, we could have chosen to make the bitOne and bitTwo variables each a byte in size, but the BASIC Stamp would still only use the their lowest bit (Bit0) as the value to transmit in the OWOUT command (due to the Mode we chose).

The OWOUT command's OutputData argument is similar to the DEBUG and SEROUT command's OutputData argument. This means data can be sent as literal text, ASCII character values, repetitive values, decimal, hexadecimal and binary translations and string data as in the examples below.

value   VAR     Byte

Init:
  value = 65

Main:
  OWOUT 0, 1, [value]                                   ' send ASCII character "A"
  OWOUT 0, 1, [REP value\5]                             ' send "A" 5x, ie: "AAAAA"
  OWOUT 0, 1, [DEC value]                               ' send "6" and "5"
  OWOUT 0, 1, [HEX value]                               ' send "4" and "1"
  OWOUT 0, 1, [BIN value]                               ' send "1000001"
  STOP

The tables below list all the available special formatters and conversion formatters available to the OWOUT command. See the DEBUG   and SEROUT commands for additional information and examples of their use.

1. Fixed-digit formatters like DEC4 will pad the number with leading 0s if necessary; ex: DEC4 65 sends 0065. If a number is larger than the specified number of digits, the leading digits will be dropped; ex: DEC4 56422 sends 6422.
2. Signed modifiers work under two's complement rules.

The 1-Wire Protocol Format

The 1-Wire protocol has a well-defined standard for transaction sequences. Every transaction sequence consists of four parts: 1) Initialization, 2) ROM Function Command, 3) Memory Function Command, and 4) Transaction/Data. Additionally, the ROM Function Command and Memory Function Command are always 8 bits wide (1 byte in size) and is sent least-significant-bit (LSB) first.

The Initialization part consists of a reset pulse (generated by the master) and will be followed by a presence pulse (generated by all slave devices). The figure below details the reset pulse generated by the BASIC Stamp and a typical presence pulse generated by a 1-Wire slave, in response.

This reset pulse is controlled by the lowest two bits of the Mode argument in the OWIN command. It can be made to appear before the ROM Function Command (ex: Mode = 1), after the Transaction/Data portion (ex: Mode = 2), before and after the entire transaction (ex: Mode = 3) or not at all (ex: Mode = 0). See the section on Mode, above, for more information.

Following the Initialization part is the ROM Function Command. The ROM Function Command is used to address the desired 1-Wire device. The table below shows common ROM Function Commands. If only a single 1-Wire device is connected, the Match ROM command can be used to address it. If more than one 1-Wire device is attached, the BASIC Stamp will ultimately have to address them individually using the Match ROM command.

The third part, the Memory Function Command, allows the BASIC Stamp to address specific memory locations, or features, of the 1-Wire device. Refer to the 1-Wire device's data sheet for a list of the available Memory Function Commands.

Finally, the Transaction/Data section is used to read or write data to the 1-Wire device. The OWOUT command will write data at this point in the transaction. A write is accomplished by generating a low-pulse of a varying width to indicate a 0 or a 1. This is called a "Write Slot" and must be at least 60 us wide. The figure below shows typical Write Slots performed by the BASIC Stamp. See the OWIN command for information on Read Slots.