Embedded programming with the Z8 Forth Microcontroller

The Z8 Forth is capable of addressing 120K of external memory: 60K for code and 60K for data. The initial 4k block of code memory is used by the Forth interperter and kernel. Data mimory can be accessed directly from a Forth program.  I will cover how to define this and other machine level prograns later.

External memory allocation begins at 1000H; program development uses 20K of RAM.  The Z8 Forth text editor and programming utilities are contained in 4K of EPROM at A000H. When loaded the utility and text editor will consume about 2.4K of memory.

Port 2 of the Z8 Forth system is dedicated to the on-board EPROM programmer. A 7407 (TTL high-voltage buffer) is used to drive the programming transistors for 2732A, 2764, 2764A type EPROM. VPP is developed by two LM317 adjustable regulators that are set to the required programming voltage. Use JP1 to select the programming voltage for 2764 (21V) or 2764A (12.6V) EPROM. A 2732A may be programmed by lower-justifying it in the ZIF socket.  JP1 may be in either position.

An 82C55-5 provides data and address communications for the EPROM. Its decoded address is at 8000H. Port A is used for the data bus (D0-D7).  Port B carries the lower half of the address bus (A0-A7) while port C carries the upper half of the address bus (A8-A15). Do not subsitute an 8255 for the 82C55-5 because the read/write setup/hold times for the 8255 are typically slower than what is required by the Z8 Forth microcontroller.

Additionally the HCT design eliminate the need for bus drivers. This system uses 250mA exclusive of programming current.