The basic features of the 8~186 Microprocessor are as follows: o 16-bit address/data bus o 8 Mhz clock o Two independent DMA channels o Programmable Interrupt Controller o Programmable 16-bit timers In addition, it can address up to I megabyte of memory in banks of 64 Kbytes and over 65,~~~ I/O ports. The CPU performs 8 and 16-bit arithmetic functions in binary or decimal. The 8~186's internal programmable interrupt control (PIC) acts as a slave to the master external PIC. It is through this master/slave setup that the microprocessor services system and internal inter r upt s. The two DMA (Direct Memory Access) channels handle requests from the disk drives and WorkNet port.
One channel is for the hard and floppy disks DMA requests; the other is for networking. MEMORY DEVICES The system provides four separate memory components to handle the various memory requirements of the system. These are the "main" memory, the system PROM, Z-8~A RAM, and z-8~A ROM. The standard main memory contains 512 Kbytes of dynamic RAM which is upgradeable to 896 Kbytes. 256 Kbytes are on the CPU board; the remainder are on two memory cards. The PROM contains the power-up tests, the debugger and various boot device drivers. The Z-8~A processing circuitry has 4K of ROM and 2K of RAM for I/O.
The ROM contains the control program and the static RAM performs temporary storage and data buffering. MEMORY MANAGEMENT UNIT (MMU) The MMU creates page memory addressing and contains a mapper and protection circuitry. The MMU circuitry is also responsible for switching the system between user and the protected supervisor mode. In user mode, the system executes the shell or application programs, such as a word processing or an accounting program, for example. In the supervisor mode, monitor programs can be run. In addition, I/O operations can only take place in the supervisor mode, and for operating systems like XENIX, the kernel must run in this state. 4-3