Assembling the ZX Spectrum Upper RAM Module

See here for more information on this device: www.worldofspec...
Installation instructions: zx.zigg.net/URR...

[@JoulesperCoulomb]

Direct Memory Access generally means the reading or writing of system memory contents by a device other than the CPU. It doesn't normally require any special support on the part of the memory. I believe it is possible for a ZX Spectrum peripheral to use DMA, though I don't think many do. Whether the upper 32K of RAM consists of the original DRAM ICs or this module shouldn't make any difference to such peripherals.

[@JoulesperCoulomb]

I hope the installation instructions are reasonably clear. Is there something in particular you aren't sure about?

[@peddersoldchap]

Since you seem not to be selling the RAM modules anymore, is there any chance of making them open source? Also, thank you for your videos.

[@RyanFaeScotland]

Wow thats some precision soldering going on.

[@retrocomputeruser]

I had a go at doing a DIY lower ram module but I am getting sporadic flickering dashes on the screen. On one spectrum they are there continuously but trying it in another they slowly disappear after powering on. I am guessing it's noise but I have fitted 0.1uF decoupling caps to both IC's. BTW it does pass ram tests and does work. Any ideas on this ?

[@JoulesperCoulomb]

It'll almost certainly be caused by addressing errors because of the rather low voltage that can represent a logic high when the corresponding output of IC3 or IC4 is low. See the compatibility note at zx.zigg.net/LRR/ . Pay attention to the specified VIH for any devices in your design that connect to the address lines. You'll want VIH to be fairly low.

[@retrocomputeruser]

@JoulsperCoulomb Thank you for your reply on this I really appreciate it. The issue seems to replicate the ULA snow effect with 6C001E-6 ULA's (I have tried 3 of them) and lasts approx 20 seconds after power up. After that the dashes slowly diminish and runs as normal apart from one ULA which is permanent but OK with DRAMS . Basically it seems the warmer the ULA gets the better. However like I said , with DRAMS installed they are ok. I have tried 2 6C001E-7 ULA's and these run perfect from the start. I will examine the datasheets and possibly connect a scope as you advise but I am mythed why it only happens on power up and only on the dash 6 variants. I have read your compatibility note and changed resistors to 470 ohm but made no difference to any version 6 ULA's. Once again Thanks for the reply and I have enjoyed your video's