Dell Inspiron charging

Part #9 of the "Roger Writes" series - December 2023

What?

I recently upgraded my laptop to a Dell Inspiron 3593 and found that it uses a smaller 4.5mm x 3.0mm 3-pin connecter. I rummaged through my stash of spare PSUs and found some HP and Dell ones with the bigger 7.4mm x 5.0mm plug, so I found a source of cheap adapters to convert from the larger to smaller connectors. Plugged in the laptop via the adapter cable, and it powers up, but won't charge! Even with a real Dell PSU (via the adapter).

Why?

After a bit of searching I found a few websites mentioning that the Dell PSUs use the 3^rd pin for a 1-wire interface that can report the power rating of the supply. Some Dell laptops (including my model) use this to decide what performance and charging profiles to use. I inspected the connector adapters that I'd brought, and although the 3^rd pin is present the socket and plug 3^rd contacts are not connected together, instead there is a pull up resistor between the plug centre pin, and +ve rail.

How?

So instead of the adapters I found a "4.5mm x 3.0mm Male Plug DC Power Adapter" that had the 3-wires visible in the on-line picture. I cut the end off of a Dell PSU (with the larger plug), and wired them to the end of the new cable. Success! The laptop charged.
Re-using a real Dell charger is fine for the AC side of things, but I use a DC:DC (12V car to laptop) adapter, so needed to fake the Dell PSU. So it was time to look at the signals.

Basic 1-wire info

The 1-wire interface is a novel design. It uses 1 signal/power wire & ground (hence the name!).
Info:

The signal line is pulled high by a resistor at the host end
This pull up resistor provides enough power for low power devices
The host and device signal to each other by pulling the line low
The host controls the signalling and timing
The host sends a reset between most commands
A reset will terminate any current command
The device sends an ACK to the reset, so the host can quickly see if any devices are connected
Because the 1-wire interface supports multiple devices, only a limited set of commands are valid after a reset (Dell only expect a single device)
The commands and data are sent in 8-bit blocks, Least significant bit first
Multi byte values are sent least signifcant byte first
To return data from the device to the host, the host signals the start of each bit, and the device pulls the line low to signal a '0'
Between bits the padding can be any duration

This is the signalling/timing:

Reset
What Level Duration Description
Pull-up: High 5us+ Power pre-charge
Host: Low 480...960us Reset
Pull-up: High Typically max of 480us Wait for Ack
Device: Low 15...60us Ack
Host Write-1:
What Level Duration Description
Host: Low 1...15us Short pulse = 1
Pull-up: High At least 60us Padding
Host Write-0:
What Level Duration Description
Host: Low 60...120us Longer pulse = 0
Host initiated read:
What Level Duration Description
Host: Low 1...15us Initiate read
Device: Low 15...45us If data is a 0
(no pulldown if data is 1)
Pull-up: High At least 60us Padding

What	Level	Duration	Description
Pull-up:	High	5us+	Power pre-charge
Host:	Low	480...960us	Reset
Pull-up:	High	Typically max of 480us	Wait for Ack
Device:	Low	15...60us	Ack

What	Level	Duration	Description
Host:	Low	1...15us	Short pulse = 1
Pull-up:	High	At least 60us	Padding

What	Level	Duration	Description
Host:	Low	60...120us	Longer pulse = 0

What	Level	Duration	Description
Host:	Low	1...15us	Initiate read
Device:	Low	15...45us	If data is a 0 (no pulldown if data is 1)
Pull-up:	High	At least 60us	Padding

Reading a Dell power supply

I used the basic 1-wire commands from a fake host to read from a real Dell PSU, I started with a "Read ID" sequence:
Fake host sends: Reset
PSU returns: An ACK
Fake host sends: 33 - This is the "Read ID" command
PSU returns: 11 63 4D 8B 00 00 00 14 - Family code, then 6 bytes of ID code, then 1 byte checksum

A family code of 11 isn't documented, but the NV RAM / EPROM / EEPROM devices all support the same basic commands, so I tried the "Read All" then "Read Data" sequence:
Fake host sends: Reset
PSU returns: An ACK
Fake host sends: CC - This is the "Read All devices" command
Fake host sends: D0 00 00 - This is the "Read Data" command, from the address 0x0000
PSU returns: 19 - (clocked by the host) This the the checksum of the read command bytes, as this is correct, it indicates that the device supports the command
PSU returns: (clocked by the host)

 
44 45 4C 4C 30 30 41 43 DELL00AC

30 39 30 31 39 35 30 34 09019504

36 43 4E 30 4B 44 38 48 6CN0KD8H

If we split this down, we get:
00: 44 45 4C 4C 30 30 DELL00 - Manufacturer ID
06: 41 43 .. .. .. .. AC.... - Device type = AC charger
08: 30 39 30 .. .. .. 090... - Power rating = 90W
0B: 31 39 35 .. .. .. 195... - Voltage = 19.5V
0E: 30 34 36 .. .. .. 046... - Current = 4.6A
11: 43 4E .. .. .. .. CN.... - Country of manufacter code
13: 30 4B 44 38 48 .. 0KD8H. - Start of the batch / serial number

Commands from a Dell laptop

It's one thing to read the PSU, using the generic 1-wire memory commands, but another to see what sequence/commands the laptop actually uses. Using the Dell PSU & 3-wire cable, it was easy to monitor the commands that the laptop issued as the PSU was plugged in.

From my laptop:
Laptop sends: Reset
PSU returns: An ACK
Laptop sends: CC - This is the "Read All devices" command
Laptop sends: D0 06 00 - This is the "Read Data" command, from the address 0x0006
PSU returns: B3 - (clocked by the host) This the the checksum of the read command bytes, as this is correct, it indicates that the device supports the command
PSU returns: (clocked by the host)
41 43 30 39 30 .. .. .. AC090...
We can see that the laptop is reading 5 bytes from byte 6, so the adapter type, and power rating!

From a friend's (older) laptop:
Laptop sends: Reset
PSU returns: An ACK
Laptop sends: CC - This is the "Read All devices" command
Laptop sends: D0 08 00 - This is the "Read Data" command, from the address 0x0008
PSU returns: 6F - (clocked by the host) This the the checksum of the read command bytes, as this is correct, it indicates that the device supports the command
PSU returns: (clocked by the host)
30 39 30 31 39 35 .. .. 090195..
We can see that the laptop is reading 6 bytes from byte 8, so the power rating and voltage!

Note: With the 1-wire disconnected from the PSU, we can see the laptop looping the Reset sequence, looking for a device to ACK it. It does this at about 500ms intervals.

Faking it!

I've used the PIC microcontrollers for a lot of projects, and an 8-bit SOIC is a good size to fake a PSU.
I chose to decode 3 commands, 0xCC "Match all", 0x33 - "Return ID bytes", 0xF0 - "Read data".
I used "FakeID" as the ID bytes, and "FAKE00AC065195033CN123456789012345678A65" for the data bytes. This claims to be a 65W, 19.5V, 3.3A supply.

The PIC code uses my portability libraries (in the open_*.h files) that should allow it to build on just about any of the 14-bit (10F, 12F, 16F) PIC devices. For the initial work I used a 16F15325 (as that what was already on my breadboard), for the final design I use a 16F15313 (which is the 8-pin device in the same family). But it should work with any device that has an internal 32MHz oscillator.

Here is the Code including the portability headers. The code includes the fake host 1-wire reader code, if you want to read from a real Dell PSU (don't forget the pull up!).
The main functions are:

void ow_device_ack_reset(void): Reset acknowledge sequence (should be within 100us or so of end of reset pulse from host)
void ow_device_reset_wait(void): Wait for a reset pulse (rejecting any too short, as they are probably clocks/data for other devices)
bool ow_device_receive_byte(BYTE *pValue): Receive byte from the host
bool ow_device_send_byte(BYTE value): Send a byte to the host (host sends the clock pulses)

Code overview:

During the sending or receiving, if a reset is detected, then the ACK is sent, and a reset flag is set.
After a reset, only the 0xCC "Read All" or 0x33 "Read ID" commands are accepted.
After a 0x33, the fake ID bytes are returned (until reset)
After a 0xCC, a 0xD0 "Read data" will be decoded, and the data returned (until reset)

Notes:

The timing after detecting the reset to sending the ACK is tight, so the code has some shortcuts
The turn around from receiving to sending is tight, especially during after the read command, so the CRC of the last address byte is calculated before it is received (we can only do this because only 00 is valid)

Building / flashing

I use MPLABX v6.05 and XC8 v2.40 with the optimiser set to /O2 (the highest for the free version!), and for the 16F15313 device it uses 119 bytes (46%) of data RAM and 670 words (33%) of instruction space. Removing the serial debug output, reduces the instruction count to 562 words (27%).
You will need a programmer to program the device, the PICKit 2 (and clones) are the cheapest, but the PICKit 3 (and clones) are not a lot more and support most devices, the PICKit 4 (no clones yet) are needed for the latest devices.

Wiring

Rather than try to power it from the 1-wire I used a 78L05 regulator to drop the 19.5V down to 5V.
I put a 470R resistor between pin 2 and the centre cable to the laptop, this is to limit any current into the PIC if the centre pin is shorted to the supply pin, and seems low enough for the signalling to be detected.

The Roger Writes series

I research / dabble with lots of things, and figured that if I write my notes here, I can quickly reference them, also, sometimes, they are useful to others!
Here is what I have so far:

Cosplay Arduino programming (RW#13 - June 2024)
ATU-100 modifications (RW#12 - February 2024)
Garage door open warning (RW#11 - January 2024)
Horizontal Halos and Vs (RW#10 - December 2023)
Faking Dell PSUs (RW#9 - December 2023)
Designing NEC2 antennas (RW#8 - November 2023)
4NEC2 antenna models (RW#7 - October 2023)
3-element cubical quad for 2m (RW#6 - September 2023)
Cobwebb Antenna dimensions (RW#5 - August 2023)
WS2812 and similar 'Smart' LEDs (RW#4 - January 2023)
Investigation and details of the AFHDS-2A protocol (RW#3 - June 2022)
Changes we've made to our caravan (RW#2 - January 2022)
Basic solar/battery/off-grid calculations (RW#1 - January 2022)
Credit card size walking robot aka Monster-Chan (RW#0 - Originally 2016 - Moved here 2022)
Why you should avoid certain number of drives with ZFS (aka why isn't my ZFS/raidz array the size I expected)
Simple way to connect a Servo to a PC (RS232 port)
Using ZFS with FreeBSD

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This page was lasted updated on Sunday, 17-Dec-2023 16:27:43 GMT