NAME

DS2408 - 1-Wire 8 Channel Addressable Switch

SYNOPSIS

8 port switch

FAMILY CODE

SPECIAL PROPERTIES

latch.0 ... latch.7 latch.ALL latch.BYTE

read-write, binary
The 8 pins (PIO) latch a bit when their state changes, either externally, or through a write to the pin.
Reading the latch property indicates that the latch has been set.
Writing "true" (non-zero) to ANY latch will reset them all. (This is the hardware design).
ALL is all latch states, accessed simultaneously, comma separated.
BYTE references all channels simultaneously as a single byte. Channel 0 is bit 0.

PIO.0 ... PIO.7 PIO.ALL PIO.BYTE

read-write, yes-no
State of the open-drain output ( PIO ) pin. 0 = non-conducting (off), 1 = conducting (on).
Writing zero will turn off the switch, non-zero will turn on the switch. Reading the PIO state will return the switch setting. To determine the actual logic level at the switch, refer to the sensed.0 ... sensed.7 sensed.ALL sensed.BYTE property.
ALL references all channels simultaneously, comma separated.
BYTE references all channels simultaneously as a single byte. Channel 0 is bit 0.

power

read-only, yes-no
Is the DS2408 powered parasitically (0) or separately on the Vcc pin (1)?

sensed.0 ... sensed.7 sensed.ALL

read-only, yes-no
Logic level at the PIO pin. 0 = ground. 1 = high (~2.4V - 5V ). Really makes sense only if the PIO state is set to zero (off), else will read zero.
ALL references all channels simultaneously, comma separated.
BYTE references all channels simultaneously as a single byte. Channel 0 is bit 0.

strobe

read-write, yes-no
RSTZ Pin Mode Control. Configures RSTZ as either RST input or STRB output:

0: configured as RST input (default)
1: configured as STRB output

por

read-write, yes-no
Specifies whether the device has performed power-on reset. This bit can only be cleared to 0 under software control. As long as this bit is 1 the device will always respond to a conditional search.

out_of_testmode

write-only, yes-no
Write "1" to this property to make sure the device has been properly initialized on startup.

The datasheet says that under some conditions the startup (power-up) will leave the device in the "testmode" state. Any problems with "Channel Access Write" will trigger this property automaticlly, but this property makes explicit initialization possible as well.

set_alarm

read-write, integer unsigned (0-333333333)
A number consisting of 9 digits XYYYYYYYY, where:

X: select source and logical term
0 PIO OR
1 latch OR
2 PIO AND
3 latch AND
Y: select channel and polarity
0 Unselected (LOW)
1 Unselected (HIGH)
2 Selected LOW
3 Selected HIGH

All digits will be truncated to the 0-3 range. Leading zeroes are optional. Low-order digit is channel 0.

Example:

100000033: Responds on Conditional Search when latch.1 or latch.0 are set to 1.
222000000: Responds on Conditional Search when sensed.7 and sensed.6 are set to 0.
000000000 (0): Never responds to Conditional Search.

LCD_H LCD SCREEN PROPERITES

This mode uses the DS2408 attached to a Hitachi HD44780 LCD controller in 4-bit mode. See DATASHEET for published details. Based on a commercial product from HobbyBoards by Erik Vickery.

LCD_H/clear

write-only, yes-no
This will clear the screen and place the cursor at the start.

LCD_H/home

write-only, yes-no
Positions the cursor in the home (upper left) position, but leaves the current text intact.

LCD_H/screen

write-only, ascii text
Writes to the LCD screen at the current position.

LCD_H/screenyc

write-only, ascii text
Writes to an LCD screen at a specified location. The controller doesn't know the true LCD dimensions, but typical selections are: 2x16 2x20 4x16 and 4x20.

Y (row): range 1 to 2 (or 4)
X (column): range 1 to 16 (or 20)

There are two formats allowed for the screenyx text, either ascii (readable text) or a binary form.

2 binary bytes: The two first characters of the passed string have the line and row: e.g. "\x02\x04string" perl string writes "string" at line 2 column 4.
ascii 2,12:: Two numbers giving line and row: Separate with a comma and end with a colon e.g. "2,4:string" writes "string" at line 2 column 4.
ascii 12:: Single column number on the (default) first line: End with a colon e.g. "12:string" writes "string" at line 1 column 12.

The positions are 1-based (i.e. the first position is 1,1).

LCD_H/onoff

write-only, unsigned
Sets several screen display functions. The selected choices should be added together.

4: Display on
2: Cursor on
1: Cursor blinking

LCD_H/message

write-only, ascii text
Writes a message to the LCD screen after clearing the screen first. This is the easiest way to display a message.

LCD_H/redefchar.0-7|ALL

write-only, binary
Redefines one of 8 user-designed character glyphs for the LCD screen (5x8 pixels).

Each byte defines a horizontal line top to bottom. All 5 pixels corresponds to 0x1F and a blank line is 0x00.

Format is 8 binary bytes.

LCD_H/redefchar_hex.0-7|ALL

write-only, ascii
Redefines one of 8 user-designed character glyphs for the LCD screen (5x8 pixels).

Each byte defines a horizontal line top to bottom. All 5 pixels corresponds to 0x1F and a blank line is 0x00.

Format is 8 hexadecimal bytes (16 characters).

LCD_M LCD SCREEN PROPERITES

This mode uses the DS2408 attached to a Hitachi HD44780 LCD controller in 8-bit mode. See DATASHEET for published details. Based on a design from Maxim and a commercial product from AAG.

LCD_M/clear

write-only, yes-no
This will clear the screen and place the cursor at the start.

LCD_M/home

write-only, yes-no
Positions the cursor in the home (upper left) position, but leaves the current text intact.

LCD_M/screen

write-only, ascii text
Writes to the LCD screen at the current position.

LCD_M/screenyc

write-only, ascii text
Writes to an LCD screen at a specified location. The controller doesn't know the true LCD dimensions, but typical selections are: 2x16 2x20 4x16 and 4x20.

Y (row): range 1 to 2 (or 4)
X (column): range 1 to 16 (or 20)

There are two formats allowed for the screenyx text, either ascii (readable text) or a binary form.

2 binary bytes: The two first characters of the passed string have the line and row: e.g. "\x02\x04string" perl string writes "string" at line 2 column 4.
ascii 2,12:: Two numbers giving line and row: Separate with a comma and end with a colon e.g. "2,4:string" writes "string" at line 2 column 4.
ascii 12:: Single column number on the (default) first line: End with a colon e.g. "12:string" writes "string" at line 1 column 12.

The positions are 1-based (i.e. the first position is 1,1).

LCD_M/onoff

write-only, unsigned
Sets several screen display functions. The selected choices should be added together.

4: Display on
2: Cursor on
1: Cursor blinking

LCD_M/message

write-only, ascii text
Writes a message to the LCD screen after clearing the screen first. This is the easiest way to display a message.

STANDARD PROPERTIES

address

r_address

read-only, ascii
The entire 64-bit unique ID. Given as upper case hexadecimal digits (0-9A-F).
address starts with the family code
r address is the address in reverse order, which is often used in other applications and labeling.

crc8

read-only, ascii
The 8-bit error correction portion. Uses cyclic redundancy check. Computed from the preceding 56 bits of the unique ID number. Given as upper case hexadecimal digits (0-9A-F).

family

read-only, ascii
The 8-bit family code. Unique to each type of device. Given as upper case hexadecimal digits (0-9A-F).

id

r_id

read-only, ascii
The 48-bit middle portion of the unique ID number. Does not include the family code or CRC. Given as upper case hexadecimal digits (0-9A-F).
r id is the id in reverse order, which is often used in other applications and labeling.

locator

r_locator

read-only, ascii
Uses an extension of the 1-wire design from iButtonLink company that associated 1-wire physical connections with a unique 1-wire code. If the connection is behind a Link Locator the locator will show a unique 8-byte number (16 character hexadecimal) starting with family code FE.
If no Link Locator is between the device and the master, the locator field will be all FF.
r locator is the locator in reverse order.

present (DEPRECATED)

read-only, yes-no
Is the device currently present on the 1-wire bus?

type

read-only, ascii
Part name assigned by Dallas Semi. E.g. DS2401 Alternative packaging (iButton vs chip) will not be distiguished.

ALARMS

Use the set_alarm property to set the alarm triggering criteria.

DESCRIPTION

1-Wire

1-wire is a wiring protocol and series of devices designed and manufactured by Dallas Semiconductor, Inc. The bus is a low-power low-speed low-connector scheme where the data line can also provide power.

Each device is uniquely and unalterably numbered during manufacture. There are a wide variety of devices, including memory, sensors (humidity, temperature, voltage, contact, current), switches, timers and data loggers. More complex devices (like thermocouple sensors) can be built with these basic devices. There are also 1-wire devices that have encryption included.

The 1-wire scheme uses a single bus master and multiple slaves on the same wire. The bus master initiates all communication. The slaves can be individually discovered and addressed using their unique ID.

Bus masters come in a variety of configurations including serial, parallel, i2c, network or USB adapters.

OWFS design

OWFS is a suite of programs that designed to make the 1-wire bus and its devices easily accessible. The underlying principle is to create a virtual filesystem, with the unique ID being the directory, and the individual properties of the device are represented as simple files that can be read and written.

Details of the individual slave or master design are hidden behind a consistent interface. The goal is to provide an easy set of tools for a software designer to create monitoring or control applications. There are some performance enhancements in the implementation, including data caching, parallel access to bus masters, and aggregation of device communication. Still the fundamental goal has been ease of use, flexibility and correctness rather than speed.

DS2408

The DS2408 (3) allows control of other devices, like LEDs and relays. It extends the DS2406 to 8 channels and includes memory.
Alternative switches include the DS2406, DS2407 and even DS2450

ADDRESSING

All 1-wire devices are factory assigned a unique 64-bit address. This address is of the form:

Family Code: 8 bits
Address: 48 bits
CRC: 8 bits

Addressing under OWFS is in hexadecimal, of form:

: 01.123456789ABC

where 01 is an example 8-bit family code, and 12345678ABC is an example 48 bit address.

The dot is optional, and the CRC code can included. If included, it must be correct.

DATASHEET

http://pdfserv.maxim-ic.com/en/ds/DS2408.pdf
http://www.hobby-boards.com/catalog/howto_lcd_driver.php
http://www.maxim-ic.com/appnotes.cfm/appnote_number/3286

AVAILABILITY

http://www.owfs.org

AUTHOR

Paul Alfille (paul.alfille@gmail.com)