docs on using ti mmu, unfinished

docs/motorola_6809_and_ti_sn74ls612_timing.md

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+# Motorola 6809 and TI SN74LS612 Timing
+
+## Motorola 6809 Timing
+Dual phase clock, E and Q. Staggered by half a clock. 
+1, 1.5, or 2 mHz. Nanosecond timing will be listed for all 3 speeds.
+
+* On Q rise, address and R/-W output is valid.
+* On E rise, data output is valid.
+* Time between Q rise and E rise is (approx) minimum 200/130/80ns and max 250/166/125ns.
+	* Time between address and R/-W output to data output.
+* On E fall, data input is read. Address and R/-W output become invalid.
+	* Data input must be valid for minimum 80/60/40ns before E fall.
+	* Output data on Q fall to ensure data input is valid.
+
+## TI SN74LS612 Timing
+Async
+
+### Write mode:
+
+* -Strobe occurs to perform write.
+* -Strobe pulse must be at least 75ns.
+* Data must be valid 75ns before -strobe fall.
+* -CS, R/-W, RS must be low at least 20ns before -strobe fall.
+* -CS, R/-W, RS, Data must be valid at least 20ns after -strobe rise.
+
+## Interface
+
+### 6809 Write to SN74LS612
+
+
+
+
+## Sources
+
+* Motorola MC6809 Datasheet, undated
+* Motorola MC6809E Datasheet, 1984
+* TI SN54LS610, SN54LS612, SN74LS610 THRU SN74LS613 Datasheet, 1981-1988