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78 bytes added ,  17:56, 11 June 2020
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In theory there needs to be 2 digital pins (UART) and 1 analog pin (JIG enable sense) accessible to the factory agent in order for JIG to work. On the Slim units, it is currently unknown where these pins might be. One theory is that there may be a USB serial hardware inside the TI charging chip. There is only weak evidence for this: the TI chip communicates with Syscon through an I2C interface and we see from pictures of the PCB that the USB data lanes go into and out of the TI chip on the Slim. This is different from the [[SN99057]] on the phat units which routes the USB data lanes in parallel (for charge sensing).
 
In theory there needs to be 2 digital pins (UART) and 1 analog pin (JIG enable sense) accessible to the factory agent in order for JIG to work. On the Slim units, it is currently unknown where these pins might be. One theory is that there may be a USB serial hardware inside the TI charging chip. There is only weak evidence for this: the TI chip communicates with Syscon through an I2C interface and we see from pictures of the PCB that the USB data lanes go into and out of the TI chip on the Slim. This is different from the [[SN99057]] on the phat units which routes the USB data lanes in parallel (for charge sensing).
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On the phat units, the [[UDC|multiconnector]] port has UART exposed on pin 6 and 7. Additionally there are pins 11, 12, and 13 that are routed directly to Ernie (seen through PCB delayering).
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On the phat units, the [[UDC|multiconnector]] port has UART exposed on pin 6 and 7. Additionally there are pins 11, 12, and 13 that are routed directly to Ernie (seen through PCB delayering). They each have a 100K pull-up resistor to 1.8V.
    
[[File:Multiconnector testpoints.png|thumb|Yellow = UDC pin 12, Cyan = UDC pin 11, Green = UDC pin 6 (RX), Magenta = UDC pin 7 (TX)]]
 
[[File:Multiconnector testpoints.png|thumb|Yellow = UDC pin 12, Cyan = UDC pin 11, Green = UDC pin 6 (RX), Magenta = UDC pin 7 (TX)]]
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We observe that without anything attached, the resistance between pin 11 and 12 is exactly 200Kohm. When the DevKit USB ethernet adapter is plugged in, the resistance between pin 11 and 12 is non-linear. One theory is that there is some sort of accessory sense based on these pins and the [[Ernie_Firmware#Voltage_Table]].
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Since the testpoints for pin 11 and 12 are close to the test points for Ernie UART, one (or both) of these pins could be used for [[Ernie_Firmware#Voltage_Table|voltage sensing]]. Below is an untested theory of what a JIG enable circuit could look like.
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[[File:Potential jig circuit.png|thumb|Possible JIG enable circuit with a 160K voltage divider.]]
    
[[Category:Syscon]]
 
[[Category:Syscon]]
 
[[Category:Devices]]
 
[[Category:Devices]]

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