80C51 dev. board design

[westfw]

Dual or Triple footprints for the RAM?  (Wide DIP, Narrow DIP, SMT)

How big is the board?  One of the things that I get hung up on, recently, is a desire to make things fit reasonably efficiently within the cheap PCB sizes available from Itead/etc.  So if you exceed 50x100mm, you're better going to 100x100mm than 80x125mm (for example.)

I have some spare 552s lying around as well.  It used to be used on the cisco Environmental Controller board, and their batteries went bad often, and the tech was replaced when flash became common...

[ealex]

The initial board was designed to fit a 150x100mm board - standard size of photoresist covered double sided board that i can process easily.
But i'll try to use itead or eurocircuits.

I've had some problems with my last order at itead: some vias  that i used to connect the bottom and top gnd layers were drilled just trough the copper layers but not trough the pcb, the silk screen alignment was way off - over some of the pads and not consistent for all boards and it had "gaps" - for example R001 appears as R_0_ where "_" is blank. I think it's my fault for these errors when I created the gerber files, but i've used the same process for other manufacturers and there were no problems with them.

The ram is IS62C256AL-45UL 28 pin plastic SOP - the part number from my schematic is wrong but the symbol and footprint should be correct.
I'll double check everything when free_electron posts the updated design files and maybe try to shrink it as much as possible.

[ealex]

hello

i've been busy till now.
i've done the following changes
 - added ft232 for usb - uart
 - added I2C RTC
 - added I2C EEPROM
 - changed board size to 150x80mm
 - added resistive networks instead of individual resistors for IO pins
 - redesign the board to fit in 150x80mm ( based on the image posted by free_electron )
 - updated design rules to match with the pcb manufacturer i've chosen

next : re-check the board against the provided rules / guidelines
should I order 2 boards ( significant price difference ) or just hope i don't ruin it ?

[ealex]

schematic

[IanJ]

Making me all nostalgic

Me too!......and following this thread closely as a result.
Here's a couple pics of one of my last projects, using the 87C51 variant.........it's a piece of test gear I built for own use back in 2004.

Good luck ealex.

Ian.

[ealex]

and the final version of the pcb, after validation from the vendor.

altium got me again: i had tons of "trace to thin" errors on the ground fill and took me a while to realize that i had the "Polygon Pour " -> "Arc Approximation" set to 0.0127mm ( the default value ).
setting that to a reasonable value fixed the problem

[nctnico]

At first glance the routing doesn't look bad. However is seems the pads on the bottom layer are missing!

[Alana]

I'd connect all ground points with trace and then pour copper onto it. Dave had issue with some boards because he didnt do that.
Apart from that - reminds me of old 8051 board i did long time ago, lots of yours is identical to mine.

[ealex]

i've messed the pdf export because of the 1Meg file limit.
i've exported each layer it it's own pdf file.

[ealex]

hello

update: I've finished the boards and got them runnig

I've made 2 mistakes that i had to fix by bodging the board, both by being and idiot and not properly reading the datasheet:
 - the chip select decoder was messed up - i had to remove all 3 chips and build another one on a small piece of prototype board. I don't know how I missed it - I've checked it several times
 - I missed the fact that during code read operations the #RD line ( connected to #OE on my board ) was not pulled low, only #PSEN -> i had to cut some traces and join #OE with #CS for each EEPROM chip ( pins 22 and 20 )

now the board seems to work: i managed to write some small assembler programs to test basic stuff : pulling GPIO's high / low , accessing the SRAM chip ( need some more tests ) and sending strings over the serial port.

For debugging I've improvised a primitive "tracer" : logic analyzer attached to the memory bus. ( i miss JTAG  )
Is there an easier way ?

Also, I've tried the sdcc C compiler but I could not get code to run - even if it seems to be OK in a simulator, maybe there is something obvious that i've been missing.

Attached: some images during board construction. ( I don't have any with the bodges )
_MG_4591: all bottom side components installed
_MG_4592: top side almost empty
_MG_4595: almost fully populated ( missing the I2C RTC and EEPROM )

[ealex]

Update:

got SDCC to work, now i'm writing basic libraries for it.
now to find a good use for the board

I've attached a picture with the bodge