{"id":4784,"date":"2023-08-11T11:48:18","date_gmt":"2023-08-11T19:48:18","guid":{"rendered":"https:\/\/wonghoi.humgar.com\/blog\/?p=4784"},"modified":"2023-08-11T11:48:20","modified_gmt":"2023-08-11T19:48:20","slug":"tl866cs-and-tl866a-recovery-mode","status":"publish","type":"post","link":"https:\/\/wonghoi.humgar.com\/blog\/2023\/08\/11\/tl866cs-and-tl866a-recovery-mode\/","title":{"rendered":"TL866CS and TL866A recovery mode"},"content":{"rendered":"\n

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I was playing around with my TL866 programmer trying to refresh the firmware and needed to get to the recovery mode. However, it seems like the recovery mode info on http:\/\/www.autoelectric.cn\/en\/note.html<\/a> is incorrect for 2014 design (the one I have). I tried the \"240\Omega\" as recommended with a decade box and it doesn’t work . <\/p>\n\n\n\n

Usually my guess that if somebody is going to set a recovery mode in a micro-controller to be enabled with some hardware path to the power supply rail with a small resistor, it’s just saying that he wants you to pull the pin high. <\/p>\n\n\n\n

The said pin is a digital I\/O line so I took it as a GPIO pin used for input (I might be wrong)<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

I measured the voltage of the said regulator with a decade box. Interesting that if I flip the resistance while the unit is on, it occasionally remembers the last state when I plug it in again! (EDIT: There is a Schmitt Trigger buffer in between. The buffer type says ST for RC1. Doh!) <\/p>\n\n\n\n

Here are some of my measurements with a decade box:<\/p>\n\n\n\n\n\n\n\n

Resistance (\"\Omega\")<\/td>Voltage at RC1 in Volts (Pin 29)<\/td>State<\/td><\/tr>
240<\/td>0.273<\/td>Autoelectric Recommended<\/td><\/tr>
100<\/td>0.614<\/td><\/td><\/tr>
50<\/td>1.132<\/td><\/td><\/tr>
45<\/td>1.246<\/td>Mid-point<\/td><\/tr>
40<\/td>1.358<\/td><\/td><\/tr>
30<\/td>1.665<\/td>Half rail of 3.3V<\/td><\/tr>
20<\/td>2.157<\/td><\/td><\/tr>
13<\/td>2.503<\/td>Logic High<\/td><\/tr>
3<\/td>3.041<\/td><\/td><\/tr>
1<\/td>3.185<\/td><\/td><\/tr>
0 (wire resistance)<\/td>3.191<\/td>Short \/ Full rail 3.3V<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

My guess is that the internal pull-ups config, open-drain changed between versions so the formula to temporarily override (fight) the default resistance that sets the logic level to 0 (basically it’s a tug of war) changed, so the suggested value no longer work consistently. <\/p>\n\n\n\n

It puzzles me why a 240\"\Omega\" which gives \"0.273V\" will be qualified as a logic high by any stretch. Even assuming \"V_{DD}=2.5V\" (the supply is \"3.3V\", but this chip has a internal \"2.5V\" regulator for data lines), \"240\Omega\" sits comfortably in the ‘low for sure’ bin given it’s \"\le 0.2V_{DD}\", which is \"0.5V\". This is how this project got started.<\/p>\n\n\n\n

\"\"
The limbo range for \"V_{DD}=2.5V\" is 0.5V to 2.0V<\/figcaption><\/figure>\n\n\n\n

Given it’s a 3.3V\/2.5V capable microcontroller, I’m confident that no manufacturer will design their CPU so that it’d be harmed by forcing a 2.5V logic level line high with 3.3V, and my guess is correct (the digital lines tolerates up to 5.5V). <\/p>\n\n\n\n

Just tying the RC1 (Pin 29 where R26 interface with) to the 3.3V rail from the regulator do the trick. No heat-ups, no blow-ups, no malfunctions.<\/p>\n\n\n\n

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I was playing around with my TL866 programmer trying to refresh the firmware and needed to get to the recovery mode. However, it seems like the recovery mode info on http:\/\/www.autoelectric.cn\/en\/note.html is incorrect for 2014 design (the one I have). … Continue reading →<\/span><\/a><\/p>\n

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