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View Full Version : Basic knowlage about GPG-ORT



Rajeshchiyyan
10-29-2011, 04:34 PM
Before you begin to use GPG-ORT,you need to know some basic knowledge about jtag.
JTAG is a debug interface which is used for debug purpose.GPG-ORT can halt and control the CPU by JTAG.So GPG-ORT can read write the flash by controlling the CPU.
There these JTAG signals(Vref,TRST,TDI,TMS,TCK,RTCK,TDO,SRST,GND) which are used during the JTAG operation.
RTCK,TRST,SRST are optional for some specific CPUs.
Vref,TDI,TMS,TCK,TDO,GND are necessary for any CPUs.

VCC
Power - Supplies VCC (5 V, 10 mA, typically) to the cable.
To target system VCC

GND
Ground - Supplies ground reference to the cable.
To target system ground

TCK
Test Clock - Drives the test logic for all devices on a JTAG chain.
Connect to system TCK pin.

TDO
Test Data Output - data from the target system is read at this pin.
Connect to system TDO pin.

TDI
Test Data Input - this signal is used to transmit serial test instructions and data.
Connect to system TDI pin.

TMS
Test Mode Select - this signal is decoded by the JTAG state machine to control test operations.
Connect to system TMS pin.

Note TRST is an optional pin in the JTAG (IEEE 1149.1) specification, and is not used by XC9500 CPLDs. If any of your non-Xilinx parts have a TRST pin, the pin should be connected to VCC.

What is PS_HOLD ?

The idea is If you canít keep phone powered on PS_HOLD will do it for you
PS_HOLD is a Test Point that designed to keep cpu powered up while supplying a battery power .

Some Power Management ICís are not able to hold dead handsets powered up and it affects operating while JTAGGing them thatís why they have PS_HOLD Points

It is required to make PS_HOLD Connection if it is exist on the pcb just to make sure everything will be stable while you are repairing the phone

There is another way to keep the phone up is : Keep pressing the power button !

How to use :

Dead Qualcomm handsets sometimes require PS_HOLD Connection on the board and purpose of this powering up the phoneís cpu by force

Basic connection is connecting PS_HOLD to VBAT with a resistor .

What is the Value of resistor that you should use :

Since VBAT Source differs on different phones which average is 3.6V to 4.2V
we should use something between 1K and 4.7K