On my RAM-only systems I simply download a 'hex' file via the 6502 serial interface into system RAM memory using the "blind monitor" function of my "loader" IC. The "blind monitor" doesn't use any system memory so you really only need to avoid I/O address space when downloading code. After downloading code into RAM, press 'reset' or enter a 'go' command to test your code. If it crashes, simply press reset and enter the "blind monitor" again. View or edit memory, download an updated file, etc...

Since the "blind monitor" doesn't use any 6502 RAM memory it's relatively easy to use my RAM-only system as an EEPROM programmer. Simply pull the HM628128 RAM chip and install an AT28C64B, AT28C256, CAT28C256, or an X28C256 EEPROM in its place. Power-up into the "blind monitor", select "Burn EEPROM", select the EEPROM type, and send a 'hex' file from Hyperterminal (using Xon/Xoff hand-shaking). You shouldn't need to specify an 'offset' for the hex file because the 8K or 32K EEPROM will present multiple images across the 64K address space, assuming of course that the 8K or 32K EEPROM is mapped in the target system on an 8K or 32K boundary, respectively.

Cheerful regards, Mike McLaren, K8LH

Note: I just added this capability to the "blind monitor" on my little Pocket 1802/5/6 project (see below).

I have a RAM only SBC with a shared memory interface to an ATmega. It pokes 100 bytes or so of loader into the shared RAM (Which is at $FF00) and the reset vector, then takes the 6502 out of reset and hopes for the best... The code runs, relocates itself to $0400 then talks to the ATmega to load the full monitor/os into $F000-$FDFF then jumps to it. ($FE00 is IO) After that, the ATmega is the serial, disk (sd card), video, etc. IO processor.

-Gordon

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Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/