Apple ][ boards -- what have I found?

On Jul 25, 17:29, Derek Peschel wrote: on To understand that, you need to have a little information about how the MOS (Machine OS) works normally (without the Tube). The whole thing is based on a very structured and comprehensive set of system calls which handle everything a user, applications programmer, or sytems programmer would want to do. The two best known are OSByte and OSWord. OSByte is used to make system calls which take few parameters, which are therefore passed in the registers: A holds the call number (determines which OSByte function you want), and X and sometimes Y pass data. The low-numbered calls mostly read or write a value in the OS variable space (eg to set serial port parameters) and the high-numbered ones are read/modify ones. Typically A holds the call number, X holds a value, and Y holds a mask. The variable is ANDed with Y and EOR'd with X (so you can set, clear, toggle, or leave unchanged any bit) and the old value is returned in X. OSWord is used for calls that need larger parameter sets. Here X and Y contain the 32-bit address of a parameter block, which may be updated by the call. There are several other sets of calls, such as OSWrCh (write a character to an output stream, eg screen or printer), OSFile (assorted filehandling functions such as open or close a file, or read a file, a byte, a directory, or whatever), OSCli (pass text to the comand line interpreter), OSEven (generate an event - a software interrupt), etc. Everythng is written to use these calls, and they work over the Tube. If the call is initiated in the 2nd Processor, its ROM knows to pass it over to the I/O processor (the 6502 in the Beeb). If it's something that involves transferring a memory block, such as the OSWORD that reads a raw disk sector into a buffer, the top part of the 32-bit address determines whether the address refers to I/O processor address space or the 2P address space. The 2nd Processor ROM only needs to know how to pass parameters to the I/O processor, how to use the FIFOs to transfer data, and be able to jump to an address in its own memory space. At reset, the MOS offers a series of service calls to each sideways ROM in turn (ie, it calls each ROM in turn, with a certain "reason code" in the A register). These calls give each ROM the opportunity to register itself as a language, a filing system, or a service provider. The ROM containing the Tube code accepts some of these calls and initialies the Tube interface. Meanwhile, if there's a second processor on the other side of the Tube, its ROM initialises its side, and when asked by the 6502 side, tells the 6502 what processor it is. Once the rest of the 6502 initialisation is complete, it will go into a loop waiting for system calls from the other side. If the other side is another 6502 (there's a 3MHz 65C02 2nd Processor), it will usually ask for a copy of the current language, which may be relocated to the top of memory, or if it's a Z80, it will ask the I/O processor to give it the contents of the first sector of a disk (and boot CP/M). other Yes, it was Ferranti. A ULA was an array of gates with no final metallisation layer pre-defined; the designer would specify the interconnections between the gates (rather like drawing a PCB layout) and that was turned into a mask which was used to lay down the metallisation in the final stages of wafer manufacture. abstract -- Pete Peter Turnbull Network Manager University of York