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TODO.md

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  • figure out if i can use the LC331632M-12 (32k words * 16 bits) sram left over from the x'eye project - should work
  • figure out what the other RAM was from the x'eye project - was it DRAM?
  • set up the SRAM-adapter for the TMS-9918 from the PDF - it's simple
  • figure out if I can use any of the ROMs i already have - yes, a 27c256 is more than enough
  • how does the original decode logic work with so few chips?
  • can i use one sanyo 16-bit ram for both the vdp and z80 since it has individual byte enables? NO
  • check the footprint against a real TMS9918 (print it out sooner rather than later)
  • can I use a knockoff U2413 as an AY-3-8910 to save some board room? are they that deeply compatible? i guess i already own an AY-3-8910. NEVER MIND IT'S AN SN76489 - already on order
  • video amp? used the one from the PDF
  • audio amp? is this too much gain? don't need one at all probably
  • reset circuit
  • cpu clock circuit ?????????????????? good enough for now?
  • how is the TMS clocked?
  • do i need to reverse a7..a0 for the TMS, or is that for data, or not at all?
  • what does RD in the SRAM-as-VRAM schematic do? they wouldn't have an extra inverter stage for nothing.
  • figure out memory decode
  • figure out IO decode
  • figure out cart decode (a subset of memory decode - bank switching)
  • what even are controllers?
  • add a bios rom
  • put in the keep-out zone for the cartridge slot (81mm x 40mm)
  • ram wraparound?
  • BIOS: what is up with the separate CE and OE in the original schematic (CE from A11?) Figure it out!!!
  • Expansion stubs (EXT_DEC_STUB, EXT_IO_STUB) need pullups or they'll fuck up
  • (CRITICAL) what is up with the -5V on the controller schematic?
  • fet to protect the power switch?
  • rca jacks around the right way?
  • why are the two 541s on the controller featuring different data bus pinouts?
  • map out the 541s
  • find some board spacers or a project case to lift this thing off a desk now that it's two sided
  • power U14, the ugly NOR that was used for the RAM
  • break out the remainder of the pins so i can use them as an inverter if need be
  • is it OK to tie CPU reset and VDP reset together? it is not
  • U21 feels unnecessary, we can probably drop it if we have leftover room on U14 in the end
  • find a replacement for the 7.15909MHz crystal (figure out how to divide a 14.31818)
  • you know what, can i just axe this entire clock section and use a 14mhz oscillator chip
  • replace the n/o jumpers with smd ones
  • size the power supply; can i get by with a 5V 2A switcher or will the voltage drop ruin it
  • power regulation - should i still have it if i have a 5V 2A switching supply?
  • replace the inline diode with a shunt to ground - rearrange the diode and fuse
  • is the SMD polyfuse on the load too small? yes, it's gone
  • weird flipflop-y section of the controller area with -5v
  • U21 (74hc04) seems not well used, lots of empty pins there
  • U22 (flipflop) not well used either
  • U18 (74ls05) is only half used
  • CRITICAL: undo the 100pF that i converted to 0.1uF on the real board (C26, C30, C31)
  • rotate the power switch
  • print out a bom for the v0.2 tag
  • abandon sanyo psram for 62256

V0.7

  • jumpers to potentially enable high address pins in ram (shh!)
  • jumper to bypass capacitor on composite output
  • jumper to switch -5V super pulldown to ground
  • controller port numbers flipped
  • unused inputs of u17 (ls05) should be grounded
  • unused inputs of u11 (ls04) should be grounded
  • u17 and u18 should probably be merged, both are ls05s and barely used
  • can u11 and u17 be merged and u11 dropped?
  • TI -5v regulator no longer available, use ICL7220?
  • bracing hole near cartridge
  • use the footprint of the de9 connector that i have, so it can be bolted (AMPHENOL 617-A009P-AJ121)
  • change the BOM to use a better de9 connector, possibly the one the footprint is based on (maybe AE10968-ND?)
  • convert power jack to USB
  • finish "making visible" all the hidden cap/resistor values
  • nice rounded edge on PCB (safety first)

V0.8

  • move the mounting hole so it doesn't interfere with the cart shell when cart is loaded and screw is installed
  • is the 10.7...mhz crystal making better video with 33pF or 56pF?
  • make 574s easier to place/solder with bigger pads