I am trying to write some software (in Turbo Pascal) to program an Atmel AT89S53 using the serial download method but I'm not having much success. I am using the first two data bits of a PCs parallel port for the inputs into the controller, and the paper-out bit on the PC as the input to the PC. I am running the controller at 4Mhz, can anyone help?!!

Any information on the exact timing ins and outs used in programming the controller would be gratefully appreciated (as the data sheet diagram is some what unclear).