Programming three microcontrollers

[muzzamil8]

Hi,

I am using three LM3S6965 microcontrollers. I have question regarding programming these microcontrollers. Can I program all three microcontroller with a single jtag connector? Firmware for each microcontroller is different.

Thanks

 

[bigdogguru]

I am using three LM3S6965 microcontrollers. I have question regarding programming these microcontrollers. Can I program all three microcontroller with a single jtag connector?

Yes, the technique is called JTAG Daisy Chaining, the exact technique is dependent on the clocking method employed:

Connecting Multiple JTAG Devices

The TCK pin is the clock for the JTAG module. This clock is provided so the test logic can operate
independently of any other system clocks. In addition, it ensures that multiple JTAG TAP controllers
that are daisy-chained together can synchronously communicate serial test data between
components. During normal operation, TCK is driven by a free-running clock with a nominal 50%
duty cycle. When necessary, TCK can be stopped at 0 or 1 for extended periods of time. While TCK
is stopped at 0 or 1, the state of the TAP controller does not change and data in the JTAG Instruction
and Data Registers is not lost.

LM3S3739 Microcontroller DATA SHEET

It should also be noted some software tools do not support JTAG daisy chaining, check compatibility with your devices programming tools.

Check your devices datasheet on specifics of JTAG daisy-chaining of your device.

BigDog

 

[mister_rf]

If a circuit contains more than one device that supports JTAG, they can be linked together to form a 'JTAG Chain'. In a JTAG chain the data output from the first device becomes the data input to the second device; the control and clock signals are common to all devices in the chain.

If your design uses multiple devices with JTAG TAP, you must either use separate connector for each device or chain devices. Generally, JTAG supports many devices in single JTAG chain, but many tools are not compatible with this feature. Check tool's documentation before you put devices into chain.

Details on page 56-65:
**broken link removed**
Maybe that reduces the required number of hardware pins on the PCB circuit, but on the other hand I think you need to do some modification for the Programmer Utility.

 

[bigdogguru]

If your programming utility does not support daisy-chained JTAG devices, you could always implement a simple jumper system to add or remove each LM3S6965 Microcontroller from the JTAG chain. It's a work around that has been successfully used in these situations.

BigDog

 

[muzzamil8]

ok

Can I use single clock source (external 8MHz) for three microcontrollers. Will microcontrollers work in parallel, i mean only one instruction of one microcontroller can be executed or instructions of all three uC be executed at the same time (parallel processing)?

 

[luben111]

Re: Single clock source for more than one microcontroller

Yes, you can make it. I personally made 20 uP to work in parallel and to execute the same program, the same instruction and the same machine cycle and I can confirm that everything works really pure synchronously

 

[muzzamil8]

My programs for each microcontroller is different. If I understand your post, you run 20 uP from a single external clock source and it worked perfectly? Is there any timing issue; I mean if three different instructions of three micrcontrollers running from three different clock sources takes 1us so will those three instructions of three uP running from single clock source take greater than 1 us or equal to 1us?

 

[bigdogguru]

Is there any timing issue; I mean if three different instructions of three micrcontrollers running from three different clock sources takes 1us so will those three instructions of three uP running from single clock source take greater than 1 us or equal to 1us?

If you connect three different processors to the same clock source, each processor with be synchronized with the other. If the instruction cycle takes 1uS on one, it will take 1uS on the other two.

BigDog

 

[muzzamil8]

ok

If I use pull up resistors on pin 5,7,9,13 and TRST instead of series resistors using jtag 20-pin connector for LM3s6965, will it function?

What is the main advantage of using series resistors for jtag programming as used in evaluation kit of lm3s6965?