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Interior of the 6502 Second Processor. The 6502 Second Processor (using a 6502C) was clocked at 3 MHz, a full 50% faster than the 6502 inside a BBC Model B, and also had 64 KB of RAM, of which typically 30–44 KB was free for application data (compared to as little as 8.5 KB on an unexpanded Model B in graphics mode, or only 5.75 KB with the disc interface).
The 6502 programming manual thus requires each ISR to reset or set the D flag if it uses the ADC or SBC instruction, but occasionally a human programmer may mistakenly omit to do this, causing a bug. For example, the Commodore 64 's KERNAL did not correctly handle this processor characteristic, requiring that IRQs be disabled or re-vectored ...
Numerous coprocessors were developed for the Tube. Most commonly seen was the 6502 Second Processor, featuring a MOS Technology 6502 processor, which allowed unmodified BBC Micro programs to run faster and with more memory, as long as they use the API for all I/O. [1] [2] The Z80 Second Processor featured a Zilog Z80 processor running CP/M, and the 32016 Second Processor featured a National ...
The BBC Microcomputer System, or BBC Micro, is a series of microcomputers designed and built by Acorn Computers Limited in the 1980s for the Computer Literacy Project of the BBC. The machine was the focus of a number of educational BBC TV programmes on computer literacy, starting with The Computer Programme in 1982, followed by Making the Most ...
The ViewSheet file format is documented on page 128 of the supplied user guide, [2] which also contains an example BBC BASIC program to print out values from a saved spreadsheet. ViewSheet takes advantage of a second 6502 processor, which triples the amount of memory available for spreadsheets, assuming the default screen mode is used (mode 3). [2]
Rather than the MOS Technology 6502 microprocessor used by the Model B, Master series models used the slightly improved 65C12. [4] Fabricated using CMOS technology, the 65C12 used less power than the 6502 and offered somewhat better performance, reportedly "almost as fast" as the original 3 MHz 6502 second processor for the BBC Micro. [5]
The processor completes the current instruction and updates registers or memory as required before responding to the interrupt. 65C816/65C802 when operating in native mode: The program bank register ( PB , the A16-A23 part of the address bus ) is pushed onto the hardware stack .
The 65C02 is a low cost, general-purpose 8-bit microprocessor (8-bit registers and data bus) with a 16-bit program counter and address bus.The register set is small, with a single 8-bit accumulator (A), two 8-bit index registers (X and Y), an 8-bit status register (P), and a 16-bit program counter (PC).