I made some feature and speed improvements to the MCL86jr board which set a new speed record for the World’s Fastest PCjr!
The MCL86jr board brings the PCjr’s total memory to 640KB and supports 8088 cycle-accurate mode as well as an “unlocked” mode which makes it around 4X faster than the IBM PC and about as fast as an IBM PC-AT!
I added two controllers to access the 512KB of SRAM. One of them runs at the 8088 bus speed which is just as fast as the memory you would plug into the side of the PCjr and runs about 1uS per access. The other controller, when selected, runs at the speed of the SRAM which is 50ns. The slower controller is used in 8088 cycle accurate mode and performs identically to the PCjr’s physical memory. The fast controller is used in “unlocked” mode and runs many times faster than the original hardware.
I also reduced some register pipeline delays in the FPGA which increased the performance to a new record.