Questions about  USART,  JTAG

USART and JTAG, two initialisms that keep showing up in conjunction with Atmega programming. What do they have to do with programming?

Are there pins on an atmega-168 that correspond to JTAG or USART ?
Does one group (USART) correspond to ISP?
Does the other group (JTAG) correspond to programming via USB to MISO, MOSI, SCK, etc ? Or is it the other way around ? Do those pins go with USART

When I program my arduino using an FTDI USB to TTL conversion device, which uses a FT232RL chip, the device is connected to TX, RX, RST(GRN) [reset output triggered by the DTR line] on the atmega, then other end of the cable connects to USB port. Is that considered JTAG, or USART or what? :-? :-[

Things get a little confusing with all of those initialisms tossed around. :o

Thank you
PO’T

Are there pins on an atmega-168 that correspond to JTAG or USART ?
Does one group (USART) correspond to ISP?
Does the other group (JTAG) correspond to programming via USB to MISO, MOSI, SCK, etc ? Or is it the other way around ? Do those pins go with USART

USART is the serial port - it shows up in the arduino as digital pins 0 and 1.
I’ll come back to JTAG but programming via USB to MISO, MOSI etc. is called ICSP or ISP - it’s atmel’s proprietary hardware programming standard
JTAG is a broader standard implemented by a variety of manufacturers. The arduino’s atmega chips support JTAG at least partially but it’s not commonly used.

When I program my arduino using an FTDI USB to TTL conversion device, which uses a FT232RL chip… Is that considered JTAG, or USART or what?

That’s using the USART - also referred to as using the bootloader.

Hope that helps.

Thanks, Bill. :slight_smile:

The arduino’s atmega chips support JTAG at least partially but it’s not commonly used.

Just done a search of the data sheet and I can’t find any reference to JTAG are you sure on this?

The arduino’s atmega chips support JTAG at least partially but it’s not commonly used.

Just done a search of the data sheet and I can’t find any reference to JTAG are you sure on this?

i’ll be honest, i thought there must be some support because the avr-dragon has a connection pattern for it. Could be it’s n/a for the 328.

Yes fundamentally JTAG has to be designed into the chip from the start. It is not normal to have JTAG support on such a simple chip. It is only needed on the more complex chips.

The ATmega328 has some “advanced” debugging capabilities, but it’s not actually JTAG (“debugwire”?) Some of the larger chips have jtag (the ones with more pins. JTAG tends to use up 4 to 6 pins…)