Editing Minimig Board v1.0 issues

== Power ==
* Suggestion: Include a +5V regulator on board OR use an ATX-style powerplug if you go Mini-ITX. The +5V regulator should be capable of providing about 1A to safely power all peripherals one might attach.

* FYI: Peak & average powerconsumption of the minimig v1 ..?
:From what I have seen the power consumption is pretty constant. All boards I've built so far consume about <B>100mA</B> (excluding keyboard/mouse).

* FYI: Any power or grounding issues?
:I did use a "local-plane" setup. I have set most IO's to slow slewrates and drive currents.

== Issue: FPGA SPI_DOUT ==
* Hardwire the patch needed to get the current board to run. Alternatively, you can also swap pin 81 (IO_L31_4/DOUT/BUSY=SPI_DOUT) and pin 79 (IO_L32P_4/GCLK0=RAM A15) on the FPGA. This way you still have four user-IOs left. You do need to change the .UCF file though and recompile the core.
<!-- Pin documentation at lower page 141 in ds099.pdf -->

* PATCH needed to get rev 1 board working:
:Disconnect net SPI_DOUT from pin 81 (IO_L31_4/DOUT/BUSY) of FPGA. 
:Connect net SPI_DOUT to pin 19 (IO_L23N_7) of FPGA (net USER3). 
:Reason: 
::Pin 81 is an output during FPGA config that blocks [[SPI]] to [[MMC]] during startup. 

== Issue: SD/MMC ==
* SPI_DOUT from SD-Card via 1k resistor and FPGA (pin81) conflicts ..?
:  A gate would be better. During normal operation, the SPI out of the MMC card is tristated by disabling the MMC, the same goes at the FPGA side (it's a tristate port). This way, they can share the SPI bus.

* The MMC card interface has a resistor based clock gate circuit around R50,R51. This should be replaced with a proper (single) gate "OR" chip. The margins on this signal are pretty tight on the current board. Also, R49 should be 0 ohm ideally to avoid problems when upgrading the PIC to a newer PIC18LF2620 or something similair. Margins are tight on that signal too atm.
* Footnote: R49 sits between SD/MMC pin7 "D0" and SPI_DOUT ([[Minimig Board v1.0 sd-card|Picture]]).

* Improvement: pin11 SW#2 (write protect) and pin12 SW#3 (no card) maybe should be utilised to avoid accidential writes and interference with spi transfers ..?
:(SW#2=open => write protect, SW#3=open => no card present)

== Issue: Possible back emf on audio output? ==
* [http://en.wikipedia.org/wiki/Headphone Headphones] may cause [http://en.wikipedia.org/wiki/Counter-electromotive_force back-emf]? (maybe supposed to be used as line-out only?)

== Issue: X1,X2 operating mode? ==
* Crystals X1 and X2 is operating in parallel or serial mode ?
:Parallel. X1 is the base PAL clock of 4.433MHz for the FPGA. X2 is the 20MHz PIC clock
:Both are working independent of each other

== Issue: Video D/A inconsistency ==
* Current Video D/A use non linear resistor ladder values.
:Current values:   4000Ω 2000Ω 1000Ω 560Ω
:Suggested values: 4220Ω 2100Ω 1050Ω 523Ω
:
:[[Minimig Video d/a resistor ladder|Video D/A resistor ladder maths & simulations]]

== Issue: SRAM ==
[http://www.amiga.org/modules/newbb/viewtopic.php?topic_id=39358&forum=8&viewmode=flat&order=ASC&start=40#forumpost460135 Dennis 070725]:<br>

* The original SRAM used [http://rocky.digikey.com/WebLib/ST%20Micro/Web%20Data/M68AW512M.pdf M68AW512M] is [http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=497-1744-ND no longer available]

* Use a single chip ram like [http://www.cypress.com/portal/server.pt?space=CommunityPage&control=SetCommunity&CommunityID=209&PageID=259&fid=37&rpn=CY62167DV30&ref=sch this] one, available at [http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=428-1860-ND digikey] for example.

* Replacing the two 512k x 16 with one 1M x 16 bit ram will do away with one chip and free RAM_SEL1

== Issue: LED resistors incorrect ==
Seems R2, R61, R62 is incorrect due that R2 is powered by +5V, while R61, R62 is powered by +3,3V but all of them use the resistance value. [[LED|See LED maths]].

== RS232 pin header wiring ==
* Connection, RS232:
:[http://www.scantips.com/serial-db9.html Internal x86-pc bracket pin mapping]

== Optimization: Clock generation ==
* You could consider using a single 20MHz oscillator and figure out how to program the DCM to generator the proper clocks, this would spare a crystal.

== Optimization: MCU & FPGA TxD sharing ==
* MCU(pic18) & FPGA TxD via AND-gate to rid of one jumper:
:Yes, no problem. However, all debug output of the PIC has to be disabled as not to interfer with the FPGA serial output.

== Optimization: Use cdrom-soundcard cable? ==
* Connection, Audio:
:[http://pinouts.ru/Multimedia/analog_creative_pinout.shtml internal x86-pc cdrom -> soundcard analogue audio pinout]
:Voltage level: (3.3V/(560ohm + 560ohm + 32ohm))*32 ohm*1000 = 91,7mV

== FYI: Power optimisation ==
[http://www.amiga.org/modules/newbb/viewtopic.php?topic_id=39358&forum=8&viewmode=flat&order=ASC&start=260#forumpost461745 Dennis 070803]:<br>
* +1.25V and +2.5V can be hooked from +3.3V to save power ?
:No gain

* Why is R42 present, it's just sitting between +1,25V and GND?
:Provides a minimum load for the LM1117.

== FYI: CPU A0 ==
* Why is the CPU pin 19 (A0) not connected to anything ..?
:The 68SEC000 is run in 16bit (selected by pin 8 (MODE=Vcc) ) mode, which means that only even addresses are used, hence the lsb address select is not needed.
:The addressing of byte wide memory addresses is done using the LDS/UDS strobes.

== FYI: SRAM UB/LB ==
* Why does the SRAM use /UB and /LB when data is 16-bit anyway?
:[http://www.amiga.org/modules/newbb/viewtopic.php?topic_id=39358&forum=8&viewmode=flat&order=ASC&start=240#forumpost461433 jkonstan 070801]:<br>
:The UB & LB strobes on the SRAM are due to data bus addressing needed for the 68K cpu. 68K CPU has UDS* strobe for upper byte lane D15-D8 access, and 68K CPU has LDS* strobe for lower byte lane D7-D0 access. When 68K does a read, D15-D0 can be accessed as a word with 68K reading what it requires off of its Databus; however, a write access on a 68K CPU requires the byte lane be qualified. When UDS* active on a write cycle, UB* on SRAM must be active. When LDS* active on a write cycle, LB* on SRAM must be active.
:
:{| class="wikitable"
|- 
|D15........D8 || D7........D0
|-
|Byte 0= Even  || Byte 1= Odd => (Word 0)
|-
|/UDS          || /LDS
|-
|etc..
|}
:
:Ie 68k writes are byte wide.

== FYI: SD/MMC pcb layout pins ==
* The SD-MMC slot has a 12-pin wide connection to pcb.
:CD/D3, CMD, GND, VDD, CLOCK, GND, D0, D1, D2, SW#1, SW#2, SW#3
:SW#1="gnd", SW#2=open=>write protect, SW#3=open=>no card present

== FYI: Fpga pin ordering ==
* Why is address/data pins to ram/cpu spread around despite dedicated board?
:Became such way to ease the PCB layout. <!-- check -->

* Why FPGA I/O pins aren't in numerical order?
:Was simple when starting out.

== FYI: FPGA config voltage ==
* FPGA configuration mode select M1,M0,M2 (pin 54, 55, 56) pins use VccAUX at +2.5V

== FYI: keyboard + mouse wire sharing ==
* Keyboard and mouse can share connection?
:Won't save data lines. <!-- check -->

== FYI: Port overvoltage protection ==
* Over/under voltage protection for keyboard or mouse port?
:It is a minimal design. The Spartan has built-in ESD protection that this design relies on. :However, monitors and TV's are notorious for blowing up video ports so extra protection has been added there!

== FYI: BAV99 is 3-pin ==
* BAV99 diodes in the schematic is 3-pin not 2-pin as can be thought.

== FYI: 15/31kHz missing reference ==
* 15/31kHz selector is missing reference designation.

== FYI: Component sizes ==
* Component size is missing.
:Seems resistor size 0805 or 0603 will fit solder pads. See also [http://en.wikipedia.org/wiki/Surface-mount_technology#Package_sizes Wikipedia: Package sizes]

== FYI: C37 value ==
* Value of capacitor C37 is 100uF/6.3V

== FYI: Video setup ==
* Video, in 15kHz mode: 
:/VSYNC = high (scart RGB enable) 
:/HSYNC = composite sync 



== FYI: Possible SD/MMC incompability ==
* Some (esp Sandisk.com) SD/MMC cards aren't standards compliant! see [http://jderogee.tripod.com/FAQ_1541.htm 1541-III FAQ]

== FYI: Seems nFPGA_SEL2 is unused ==
Neither MCU or FPGA firmware sources reference this line in any active way. This could free one I/O.<!-- Confirm with Dennis -->

== FYI: I/O mode alternative ==
LVTTL could be used instead of LVCMOS33. No cons/pros found at this time.

== FYI: Xilinx Place & Route limitation ==
[http://www.xilinx.com/ise/products/webpack_config.htm Xilinx ISE Webpack device support]<br>
:Free version supports Spartan3 XC3S50 - XC3S1500 <!-- Has implication for m68k in hdl or expansions -->