describe how a JTAG connection is used to test the circuitry in a chip using just 5 pins
JTAG is used as a synonyme for the boundary scan protocol, see
- https://en.wikipedia.org/wiki/JTAG#Boundary_scan_testing
- https://en.wikipedia.org/wiki/Boundary_scan
It was the Joint Test Action Group (JTAG) who originally devised this protocol for testing circuitry around chips.
Besides this original purpose, the same protocol is used to program and debug CPUs, FPGAs etc.
In order to use JTAG, you need an adapter device that supports the circuitry you would like to test/debug.
[...] using just 5 pins
You are wondering how to test the entire chip through "just" 5 pins? To get a rough idea, think of a shift register similar to UART and SPI (but keep in mind that JTAG is notably more sophisticated).
Related
I'm using PySerial to communicate to some devices over RS485 multi-drop. I am bit-banging the DE signal to enable transmission before sending a packet and releasing it at the end.
The problem is that the time for release varies, especially under processor load, and the responses from the devices get clobbered (and aren't received).
I know PySerial has RS485 support, but from everything I've read about my embedded SBC (NXP iMX6 Dual), the RTS signal is not available on the GPIO connector. I just have arbitrary GPIO to use.
Is there a way to map an arbitrary GPIO signal to the RTS functionality so that the Linux tty drivers will assert/deassert my desired GPIO pin?
The following statement gives me some hope (https://www.kernel.org/doc/html/v4.17/driver-api/gpio/drivers-on-gpio.html)
"""
... there are special GPIO drivers in subsystems like ... the TTY serial subsystem to emulate MCTRL (modem control) signals CTS/RTS by using two GPIO lines.
"""
There seems to be some kind of support for in the tty driver for /dev/ttyimxN devices.
https://github.com/torvalds/linux/blob/v4.14/drivers/tty/serial/serial_mctrl_gpio.h
https://github.com/torvalds/linux/blob/v4.14/drivers/tty/serial/imx.c
unsigned int have_rtsgpio:1;
But how can I set this up with PySerial?
How can I specify the GPIO port to use (if at all)?
Thanks for any help !!
EDIT
I've found info in the kernel sources that match the kernel on my board. This describes how to specify the gpio for modem control emulation (software control, instead of hardware control).
https://github.com/ADVANTECH-Corp/linux-imx/blob/adv_4.14.98_2.0.0_ga/Documentation/devicetree/bindings/serial/serial.txt
So it seems possible by changing the device tree sources and making a new device tree blob for my system.
This should all be independent of pyserial.
I'm not sure if this can be set/overridden at runtime with an ioctl, which would be handy (instead of having to muck around with kernel sources and building device tree blobs, etc).
I tried to find an answer to this question by searching SDIO which is related to my question based on Silicon Labs naming of data channels. However, I was flooded with topics related to the SDIO protocol for serial comms with an SD memory card - a totally different concern.
I want to interface a PIC MCU (SPI bus) with Silicon Labs FM TX/RX 47XX chips which describe a serial control interface and the multiple ways to use it - what they call 2-wire (basically I2C) or what they call 3-wire and refer to as "SPI". The 3 lines are SLCK, SEN and SDIO (clock, enable, and data input/output half-duplex over the same wire).
My problem is that SPI is full duplex capable - TX and RX simultaneously. Even though every implementation I've seen of this is really half-duplex - send then receive - the hardware is wired with SDI/SDO or MISO/MOSI or called whatever lines in the SPI module; a separate data IN and a data OUT wire. Along with SCLK and SEN (clock and enable).
I'm not sure how to wire this up - and whether it will work. Do I wire both the SDI and SDO pins of the PIC (SPI module) to the same SDIO on the Si47XX? Since the Si47XX is half-duplex that would make sense; but I've never seen the two lines tied on an SPI interface. Not sure if the pins are always Hi-Z for example and I don't want to fry something out. Would I need to add pull ups/downs?
Oddly, I can't seem to find an actual wiring diagram of such a case. When I search 3-wire SPI I always get examples where SEN is tied since only one slave device is being used - not my situation. Any advice would be - as always - greatly appreciated.
-Rick
One can interconnect SPI and 3-wire devices using the following schematic. It does not matter which device is master and which is slave.
SPI device 3-wire device
----+
SDO |--/\/\/\-+ 3k
| | +---
SDI |---------*--------| SDIO
| |
SCK |------------------| SCK
SEN |------------------| SEN
----+ +---
If a 3-wire device is in reception state, then SDO signal comes via resistor to (Hi-Z) SDIO pin and back to SDI pin.
If the 3-wire device is in transmission state, then SDIO output overrides SDO value.
The example of such connection one can see in FTDI datasheet for FT2232H, page 37 (Figure 4.1RS232 Configuration) — 93С46 to FT2232H connection.
At lower SPI frequencies one can use higher resistor value for lower overriding current. It's depend also from traces length but in usual cases 3k is in very good marging for frequences up to 2 MHz.
p.s. It seems that the question is not about programming. Could it be moved to electronics.stackexchange.com?
I want to use a sensor with one-wire protocol, the matter is which way of using this protocol is optimized and more rational? over usart or using bit banging?
if it is important I'm using am2305 and stm32fxx microcontrollers.
I'm prefer to use USART+DMA with one buffer for transmit and receive. And I think this choice depends on your skill and requierements of your project.
There many ways to implement one-wire protocol.
exti interrupts + timer base mode
timer input capture + dma
usart interrupts
usart (err interrupts only) + dma
All of them have thier advantages and disadvantages:
busy or free pins
busy or free periferals (tim, usart)
busy or free dma channels
lower or higher frequency of interrupts in programm
easy or hard for implement it
I have different projects where work first and last methods listed above.
You must know which method is preferred for you and your project.
I am trying to send/retreieve data from/to FPGA using Matlab. I connected FPGA using Virtual com port. Now how to send data from Matlab to FPGA or read data of FPGA ?
FTDI 2232H is on the FPGA as well. I connected external LED's and switches on the I/O ports of the FPGA.
I am new in this field, so want some guideline to start communication b/w MAtlab and FPGA:
I tried following code:
s1= serial('COM9')
fopen(s1)
. Is it the right way to communicate ? Kindly guide. thanks
FPGA's are configured using a Hardware Description Language (HDL) such as Verilog or VHDL. These languages let you specify how the switch configuration within the FPGA, which in turn lets you construct your custom digital logic and processing system.
The HDL Coder Toolbox in Matlab lets you design and prototype your custom logic using higher-level functions, which are then translated into HDL and can be be used to directly program your chip. This tutorial describes the process in detail.
If you already have a design implemented on your FPGA and want to communicate with that implementation, you would use Matlab's serial port communication functions. The exact protocol will depend on the interface you have implemented.
Some intermediate debugging steps I find helpful:
Verify that you can send serial port data from your computer. In Windows XP, you can do this easily with HyperTerminal, and hooking up a scope to the output pins of your serial cable. Set up a trigger to capture the event. For Windows 7 and newer, you'll need to download a HyperTerminal client.
Repeat this same process with Matlab. Using a scope, verify that you see the serial port signal when sent from Matlab, and that the output matches the results from step 1. Again, set up a scope trigger to capture the event.
Now connect the serial cable directly to the FPGA board. Modify your HDL to include a latch on the serial input that displays the output on the LED's. Verify that your board initializes to the correct LED state, and that the LED state changes when you send the serial message.
Lastly, verify that you are interpreting the message correctly on the FPGA side. This includes making sure that the bit-ordering is correct, etc. Again, the LED outputs can be very helpful for this part.
The key here is to take small, incremental steps, physically verifying that things are working each step of the way.
I'm working on a project where I want to install a photodetector circuit to a computer through some sort of interface (preferably USB). However, since I am new at this so I do not know in what direction that I should approach this problem on. Assuming I have a photodector circuit with a USB connection, does the "interfacing" require only writing the device driver? Or do I need to do any additional work? Please advise if I am overlooking something. Thanks!
The easiest way to communicate with your computer would be using an integrated circuit that does all the communication for you. Take a look e.g. at the FTDI FT232 Chip. It is extremly simple to use as it emulates a virtual COM port in the basic mode (USB drivers for all major platforms are included). So the only thing you would have to do on the PC side would be writing to the serial (COM) port.
Then your microcontroller circuit can simply communicate with this chip via UART, which is supported by almost every controller (e.g. Atmel ATmega series).
Alternatively you can simply use your real RS232-Port, but many modern computer don't have such a port anymore.
The simplest one possible is obviously through the LPT port.
Out of its 25 pins, 8 are available for input/output and can be connected to any sort of electronic device... including your custom PCB.
It takes simple values :
0 - 00000000
1 - 00000001
2 - 00000010
3 - 00000011
.
.
.
.
255 - 11111111
Check this out for pinouts http://t3.gstatic.com/images?q=tbn:ANd9GcTQy9wmJzTBVAJjMwEdavBoypcwFOXwQ-sA5E2aR-dBLyn1_DDRfg