standards for in circuit programming pads - Page 1
Forum section: electronics / general

author: Avi
author_rank: Contributor
timestamp: May 12, 2016, 01:13:16 pm
content: Are there any standards for in circuit programming pads?size?shape?pad spacing?location on board?pad ordering?supply pins required as pads?Also, how are these details given to the PCB manufacturer?What about flashing software, and how to use it, and what OS it requires?

author: mmagin
author_rank: Frequent Contributor
timestamp: May 12, 2016, 03:25:05 pm
content: Is this the kind of think you're looking for?http://www.tag-connect.com/Beyond that, it's just a footprint in your pcb design software that provides various features at various layers. There might be some best practices as far as designs you're making that a contract manufacturer will assemble and program though, I'm sure others can fill in more there.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 12, 2016, 05:13:03 pm
content: Well, I'd recommend test points at least 30 mils o.d. (bare SMT pads, or vias / TH pads) and 60 mils spacing (center to center).You can place them pretty much anywhere. It might be handy to arrange them in patterns. TAG-Connect is a good example; you can use the connector-of-nails to program it during development, or a bed-of-nails test fixture in production.Often you'll see a row of pads which run to obvious locations (power, ground, microcontroller), either a serial or TWI or JTAG port, or something like that. For a production test fixture, there's no reason to arrange them that way, it's just fun.Tim

author: uncle_bob
author_rank: Unknown
timestamp: May 13, 2016, 12:02:05 am
content: Quote from: Avi on May 12, 2016, 01:13:16 pmHiLet's back up a bit:1) What are you trying to program on your board?2) Do you have room on the board for the "normal" programming connector(s)?3) Your PCB assembly house *may* not do programming at all. Have you checked with them?The how and the why of the above questions: Different parts require very different test / alignment and programming connections. What you might need on a microwave amplifier board is very different than what you need on a refrigerator control board. In both cases, you may spend a lot of time shooting debug loads into the board. Being able to do that with normal tools can be a giant time saver. The low cost guys around here just put boards together. Any testing / debugging / alignment past that is up to you. I would *not* want to do it any other way ....Bob

author: Avi
author_rank: Contributor
timestamp: May 16, 2016, 01:10:22 pm
content: Quote from: uncle_bob on May 13, 2016, 12:02:05 amESP8266 (ESP-12)Quote from: uncle_bob on May 13, 2016, 12:02:05 amwell, lots of room, but what do you mean "normal", as in an ftdi programmer sort of pad arrangement?Quote from: uncle_bob on May 13, 2016, 12:02:05 amthey do, but i dont know what they use, im going to assume they have some sort of bed of nails or pogo pins

author: uncle_bob
author_rank: Unknown
timestamp: May 16, 2016, 08:35:29 pm
content: Quote from: Avi on May 16, 2016, 01:10:22 pmHiIf they already have gear that will program that very non-standard device, I'd simply ask them what it is. Most MCU's, modules, and FPGA's have defined connectors that are used to program them. A 10 pin 0.1" spaced JTAG connector is one very common example. The programmer mates up with it and shoots JTAG commands into the device chain on the board. Since there are only 4 important pins (plus power and ground), there are abbreviated versions. The common approach is to lay out for the standard connector. That way everybody knows what they need to hit and there are no added costs. If you put in a grid of pads for a bed of nails, expect for them to charge you an added cost for the custom fixture to hit your pad locations. If you decide to not populate the connector location in production, they already should have a way to hit the pads without much of a charge.Bob

author: KL27x
author_rank: Super Contributor
timestamp: May 16, 2016, 10:05:54 pm
content: 0.05" is pretty much the practical minimum for spacing, FYI. The physical size you can practically make pogo pins is a limiting factor. The minimum center to center distance is specified by the pin, and unless you want to get really exotic and pricey on the cost of the interface, 0.05" is the minimum limit.Beyond that, observe the usual. And don't stick the header between two tall capacitors, etc. Pogo pins only extend maybe 1/4", plus or minus, depending on how the interface is designed.

author: Avi
author_rank: Contributor
timestamp: May 18, 2016, 07:11:20 pm
content: Quote from: uncle_bob on May 16, 2016, 08:35:29 pmWhat is that, exactly?

author: Gribo
author_rank: Frequent Contributor
timestamp: May 18, 2016, 07:38:36 pm
content: There are too many 'standard' programmer connectors out there, starting with 0.1", 2x7 headers, through 4 pins at 1mm pitch to Miktor style headers and footprints. If there is a common enough programmer for the ESP (J-link?) You can use that programmer's header, which allows you to plug the flat cable's connector directly.

author: uncle_bob
author_rank: Unknown
timestamp: May 19, 2016, 12:16:13 am
content: Quote from: Avi on May 18, 2016, 07:11:20 pmHiOn a normal chip or module, it's a well defined connector that goes along with the device. For the weird part you have it's unclear. If your assembly house is already fully setup to deal with a part that unusual, they probably already have a connector associated with it.Bob

author: Avi
author_rank: Contributor
timestamp: May 19, 2016, 06:06:20 pm
content: So basically Id have to ask the factory what pad arrangement they would use for a serial link?

author: uncle_bob
author_rank: Unknown
timestamp: May 19, 2016, 11:29:08 pm
content: Quote from: Avi on May 19, 2016, 06:06:20 pmHiThat's by far the lowest cost way to do it. Unless there is a well defined (by the chip guys) pad layout, guessing will cost you money.Bob