A status, or condition code register (CCR) stores the status results of computation: carry, zero, overflow, and so on. They have two accumulator registers (A, B) and one index register (X) as well as a stack pointer (SP), and program counter (PC). Plus, writing one is a great way to learn about a CPU.ĬPUs in the 6800 family are simple. On a whim I decided to write a disassembler in Perl with all the features that were lacking from other offerings. While I use nice GUI software to tune the parameters, I wanted to peer into the code that is executed on a 1MHz Motorola 6800-family CPUs with a paucity of memory. Only recently has my 1986 Jeep Grand Wagoneer benefited from this technology when I retrofit an 80's GM 1227747 ECM, throttle body, and all the fixin's. They employ complex algorithms to properly meter fuel under myriad engine and environmental conditions. DIYers retrieved machine code, disassembled it, and reverse engineered code and hundreds of parameters 15 years ago.įuel injection computers interface with fuel pump relays, fuel injectors, ignition modules, coolant, throttle, oxygen, and pressure sensors. ![]() ![]() This is the tale of how I wrote a Perl disassembler for the Motorola 6801 CPU to learn how the fuel injection computer that I installed onto my Jeep works.Īlmost 200 pages of source code and data create code to run late-80's GM fuel injected engines.
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