Using a 28F010 Flash Device</b> by Pete McCollum

The 28F010 is a 128K X 8 device that can be programmed randomly
one byte at a time, but must be erased in it's entirety.
Hardware connections to the 6502 are essentially the same as with
other 'standard' memory devices.
The 28F010 is available in two different packages, a 32-pin DIP and PLCC.

Pinouts for the 28F010 Flash Device.
After connecting the power lines, address and data busses, and chip
select, you must generate the OE and RW signals needed to talk to memory
devices.

Logic to generate /OE and /RW signals.

The method shown is essentially the same as that used
on the KIM-1. The CE signal is generated through address selection,
the same as with any other I/O or memory device.

Since a 6502 cannot address 128K directly, the upper address
bits can be either tied to ground, or controlled from a parallel
I/O port (such as a 6522).

Note that the 28F010 requires a +12 volt source on pin 1 (Vpp)
during any programming or erasing operation, in addition to the
normal +5 volts on pin 32.

Below is some code for programming and erasing a 28F010 flash.  You may
view it here.

Consult the device data sheet for complete info on programming
and erasing. It's a good idea to disable interrupts (SEI) during
the process.
	; Flash a single byte, using the data in FDA, and the addr in
	; FRADLO/HI. FCNT will contain how many more times we would
	; have tried it. If it fails, FFDA contains the data that was
	; read back. Nothing is preserved.
FLASHB:
	LDY #$19        ; Max of 25 retries
	LDX #$0         ; init X
FLOOP:
	LDA #$40        ; send Program Byte command
	STA (TOADLO,X)
	LDA FDA         ; send the data to be programmed
	STA (TOADLO,X)
	; The next 4 instructions are a time delay: a total of
	; around 10us with a 1.8 MHz clock. The exact amount isn't
	; critical, but should be *at least* 10us.
	ROR 0
	ROL 0
	NOP
	NOP
	; The next 2 instructions count as part of the delay:
	LDA #$C0         ; send the Verify command
	STA (TOADLO,X)
	LDA (TOADLO,X)   ; read the programmed byte
	CMP FDA          ; is it the same?
	BEQ FDONE        ; yes, we're done
	DEY              ; no, try again
	BNE FLOOP
FDONE:
	STY FCNT         ; save the number of loops
	STA FFDA         ; save the last data we read
	LDA #$0          ; send the Read Mode command
	STA (TOADLO,X)
	RTS

	; Erase the flash. The flash is 128K, but all we
	; can address is 32K, so just erase that (really the
	; entire device is being erased, but we are only verifying
	; the first 32K). Nothing is preserved.
ERASE:
	LDX #$00
	LDA #$00        ; Init our temp storage
	STA FDA         ; We will program all bytes to #$00 first.
	STA TOADLO      ; Flash starts at address $6000.
	LDA #$60
	STA TOADHI
ERASE1:
	JSR FLASHB      ; Program a byte
	INC TOADLO      ; INC to next address
	BNE ERASE1      ; No wrap - go do next address
	INC TOADHI      ; Wrapped - INC hi byte
	LDA #$E0        ; Did we go beyond 32K ?
	CMP TOADHI
	BNE ERASE1      ; No, go do this address
	LDA #$0         ; Yes, get ready to erase
	STA TOADLO
	STA ECNTLO      ; erase-cycle counter
	STA ECNTHI
	LDA #$60        ; back to the beginning
	STA TOADHI
ERASE2:
	LDA #$20        ; send the Erase command
	STA (TOADLO,X)
	STA (TOADLO,X)  ; we must send it twice
	LDA #$3         ; Delay for about 12 ms (10 ms required)
	JSR DELAY       ;
ERASE3:
	LDA #$A0        ; send the Erase Verify command
	STA (TOADLO,X)
	LDA (TOADLO,X)  ; is the data #$FF ?
	CMP #$FF
	BNE ERASE4      ; no, go INC counters and try again
	INC TOADLO      ; yes, INC the address counter
	BNE ERASE3
	INC TOADHI
	LDA TOADHI
	CMP #$E0        ; are we beyond 32K ?
	BNE ERASE3      ; no, do another erase cycle
EDONE:
	LDA #$0         ; we're done - send the Read Mode command
	STA (TOADLO,X)
	RTS
ERASE4:
	INC ECNTLO      ; INC the erase-retry counter
	BNE ERASE2
	INC ECNTHI
	LDA ECNTHI
	CMP #$4         ; have we done more than 1000 cycles?
	BEQ EDONE       ; yes - quit (failure)
	BNE ERASE2      ; no - do another erase cycle