DS2740(3)

💖 DS2740 — High-Precision Coulomb Counter 💖

okay bestie, gather round, because we're talking about the DS2740, aka the High-Precision Coulomb Counter, and she is lowkey iconic. this is a page from the One-Wire File System manual (that's OWFS, section 3 of the manuals) and it's all about one specific lil chip in the 1-wire fam. no cap, she counts coulombs and she does it precisely. let's get into it 🫶

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✨ SYNOPSIS ✨

so the vibe here is Voltage and Switch 💅

36 [.]XXXXXXXXXXXX[XX][/[ memory | PIO | sensed | vis | vis_B |
volthours |
smod |
address | crc8 | id | locator | r_address | r_id | r_locator | type ]]

that's the directory shape you'll be poking at, bestie. memorize it or don't, but she's the whole map 🗺️

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🌈 FAMILY CODE 🌈

36

that's her number. that's how you know it's her. periodt. 💅

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🎀 SPECIAL PROPERTIES 🎀

these are the main-character properties, the ones that make this chip this chip.

• memory — read-write, binary. this gives you access to the full 256 byte memory range. heads up tho: a LOT of that space is reserved or has special uses — the user space is the page area. check the DATASHEET for the full memory map, bestie, because this space is not all yours to play in 🫣
• PIO — write-only, yes-no. she controls the PIO pin, which lets you do external switching. writing "1" turns the PIO pin on (conducting). writing "0" makes the pin non-conducting. if you wanna know the logical state of the voltage, read the sensed property — and note that sensed reflects the current voltage at the pin, NOT the value you sent to PIO. also! PIO will also be altered by the power-status of the DS2670 — see the datasheet for details. not me warning you twice, but here we are 💀
• sensed — read-only, yes-no. the logical voltage at the PIO pin. only actually useful if you've set the PIO property to "0" (non-conducting). value will be 0 or 1 depending on the voltage threshold. simple. clean. slay ✨
• vis — read-only, floating point. the current sensor reading (unknown external resistor). it measures the voltage gradient between the Vis pins, and the units are in Volts. the vis readings get integrated over time to give you the volthours property. the current reading is derived from vis assuming the internal 25 mOhm resistor is employed — and there is no way to know this through software. so like. she's giving mystery, she's giving ambiguity, and we just have to live with it 😭
• vis_B — read-only, floating point. also a current sensor reading (unknown external resistor), also measures the voltage gradient between the Vis pins, also in Volts. same deal: vis readings integrate over time → volthours property. but vis_B is from a different tuning of the DS2740 (3) chip, with faster sampling and lower resolution. and again — there is no way to know this through software. two mysteries for the price of one, bestie 💀
• volthours — read-write, floating point. the integral of vis over time. units are in volthours. it's math, it's cute, it's cumulative 🔥

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🦋 OBSCURE PROPERTIES 🦋

just the one, and she's mysterious.

• smod — read-write, yes-no. bit flags corresponding to various battery management functions of the chip. see the DATASHEET for details of the identically named entries. in general, writing "0" corresponds to a 0 bit value, and non-zero corresponds to a 1 bit value. this is also the default power-on state for the corresponding properties. iykyk 👑

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🌸 STANDARD PROPERTIES 🌸

every 1-wire device has these, so this is the shared girlhood of the whole family.

• 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. two formats, one queen 💅

• 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). she's the vibe check for your ID ✨
• 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 the 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 the 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 there is no Link Locator between the device and the master, the locator field will be all FF. r_locator is the locator in reverse order. it's giving where are you actually, bestie 📍

• present (DEPRECATED) — read-only, yes-no. is the device currently present on the 1-wire bus? > ⚠️ heads up: this one is DEPRECATED. she's retired, she's a legend, she's not the move anymore.
• type — read-only, ascii. part name assigned by Dallas Semi. e.g. DS2401. alternative packaging (iButton vs chip) will not be distinguished. so like, don't come for her about the outfit, she only tells you the name 🎀

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🚨 ALARMS 🚨

None.

no alarms. no chaos. we love a calm queen. 😌

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💜 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. one wire doing two jobs? multitasking queen. 💅

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. spicy 🔐

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. main character energy is the master, obviously 👑

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

🗂️ OWFS design

OWFS is a suite of programs 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 represented as simple files that can be read and written. it's giving everything is a file and honestly? iconic 🦋

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. periodt. 💖

🔋 DS2740

the DS2740 (3) is a class of battery charging controllers. this chip measures voltage and volthours, and has a pin that can be used for control. tiny chip, big responsibilities, we stan 🫶

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🌟 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. (yes bestie, i know, count the digits, that's how it is in the source, don't come for me 🙈)

the dot is optional, and the CRC code can be included. if included, it must be correct. no shortcuts, no typos, she will not forgive you 💀

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📄 DATASHEET 📄

http://pdfserv.maxim-ic.com/en/ds/DS2740.pdf

go read it, bestie, it's the lore 🍓

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👀 SEE ALSO 👀

💻 Programs

owfs (1) owhttpd (1) owftpd (1) owserver (1) owdir (1) owread (1) owwrite (1) owpresent (1) owtap (1)

🧪 Configuration and testing

owfs (5) owtap (1) owmon (1)

🗣️ Language bindings

owtcl (3) owperl (3) owcapi (3)

⏰ Clocks

DS1427 (3) DS1904 (3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3) DS2417 (3)

🆔 ID

DS2401 (3) DS2411 (3) DS1990A (3)

💾 Memory

DS1982 (3) DS1985 (3) DS1986 (3) DS1991 (3) DS1992 (3) DS1993 (3) DS1995 (3) DS1996 (3) DS2430A (3) DS2431 (3) DS2433 (3) DS2502 (3) DS2506 (3) DS28E04 (3) DS28EC20 (3)

🎛️ Switches

DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3) InfernoEmbedded (3)

🌡️ Temperature

DS1822 (3) DS1825 (3) DS1820 (3) DS18B20 (3) DS18S20 (3) DS1920 (3) DS1921 (3) DS1821 (3) DS28EA00 (3) DS28E04 (3) EDS0064 (3) EDS0065 (3) EDS0066 (3) EDS0067 (3) EDS0068 (3) EDS0071 (3) EDS0072 (3) MAX31826 (3)

💧 Humidity

DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)

⚡ Voltage

DS2450 (3)

🧱 Resistance

DS2890 (3)

🧬 Multifunction (current, voltage, temperature)

DS2436 (3) DS2437 (3) DS2438 (3) DS2751 (3) DS2755 (3) DS2756 (3) DS2760 (3) DS2770 (3) DS2780 (3) DS2781 (3) DS2788 (3) DS2784 (3)

🔢 Counter

DS2423 (3)

🖥️ LCD Screen

LCD (3) DS2408 (3)

🔐 Crypto

DS1977 (3)

🌀 Pressure

DS2406 (3) TAI8570 (3) EDS0066 (3) EDS0068 (3)

🌊 Moisture

EEEF (3) DS2438 (3)

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🌐 AVAILABILITY 🌐

http://www.owfs.org

come thru, bestie, the whole project lives there 🫶

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✍️ AUTHOR ✍️

Paul Alfille (paul.alfille@gmail.com)

the legend herself. thank you for your service, queen 👑

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okay so that's the whole page!! every property, every flag, every code, every reference — all of it, untouched, just wrapped in glitter ✨ this was OWFS Manpage, dated 2003, for DS2740(3) 💖 go forth and count some coulombs, bestie, and remember: the dot is optional but the CRC must be correct. mwah 💅🎀🦋