Z-8681 Microcomputer
Technical Manual
November 1984

I searched the internet but could not find any decent description of a technical manual for the Z8 Microcomputer in HTML or PDF format. So I decided to donate some time by retyping part of my paper Z8 manual. I have skipped the sections that were irrelevant to the Z8681 device.

Please keep the DATE of this publication in mind!

Chapter I: Z8 Family overview.

1.1 Introduction.

This chapter provides an overview of the architecture of the Z8 family of products, with particular emphasis on those features that set this microcomputer apart from earlier microcomputers.
Detailed information about the architecture, address spaces and modes, instruction set, external interface, timing, input/output operations and interrupts can be found in subsequent chapters of this manual.

1.2 Features.

The Z8 microcomputer introduces a new level of sophistication to the single-chip architecture. Compared to earlier single-chip microcomputers, the Z8 offers faster execution, more efficient use of memory, more sophisticated interrupt, input/output and bit-manipulation capabilities and easier system expansion.

Z8 products offer the standard on-chip functions of earlier microcomputers, including:

Beyond these basic features, the Z8 family offers such advaced characteristics as: All members of the Z8 family are variations of the basic Z8 microcomputer, the Z8601 and Z8611. The Z8 family includes a development device (Z8612), a ROMless version (Z8681, Z8682), a BASIC/Debug interpreter (Z8671), a protopack emulator (Z8601, Z8613) as well as the basic Z8601 and Z8611 microcomputers.
These products offer all the the parts and development tools necessary for systems development (both hardware AND software prototyping) field trials (pre-production) and full production.
For prototyping and pre-production, where code flexibility is important, the Z8603 and Z8613 protopack 2K and 4K EPROM based versions are the most appropriate. The ROM based Z8601 and Z8611 microcomputers are used in high-volume production applications after the software has been perfected. For ROMless applications three versions are available: the 40 pin Z8681 and Z8682 and the 64 pin Z8612. In addition there is a military version of the Z8611 4K ROM chip available in both 40 pin ceramic or 44 pin leadless chip carrier packages.

The Z8671 MCU is a complete microcomputer preprogrammed with a BASIC/Debug interpreter. This device, operating with both external ROM or RAM and on-chip memory registers, is suitable for most industrial control applications, or whenever fast and efficient program development is necessary.

The Z8 MCU is well-suited for dedicated control applications in real-time mode. Since speed is a key consideration in such applications, the Z8 family is available in both 8 and 12 MHz versions supported by either of two development modules or the Z-SCAN 8. The Z-SCAN module provides ICE (In Circuit Emulation) capabilities.

1.2.1 Instruction set.

The Z8 instruction set, consisting of 43 basic instructions, is optimized for high code density and reduced execution time. The 47 instruction types and six addressing modes -together with the ability to operate on bits, nibbles, BCD digits bytes and words- make for a code-efficient and flexible MCU.

1.2.2 Architecture.

The Z8 architecture offers more flexibility and performance than previous A/B accumulator designs. All 128 general purpose registers, including dedicated I/O registers, can be used as accumulators. This eliminates the bottleneck commonly found in A/B devices, particularly in highspeed applications such as disk drives, printers and terminals. In addition, the registers can be used as address pointers for indirect addressing, as index registers or for implementing an on-chip stack. Speed of execution and smooth programming are supported by a 'working register area' 4-bit register addresses.
Table 1-1 lists the basic characteristics of the members of the Z8 family. As shown, the major differences between the products are in their physical packaging and the manner in which address space is handled. An overall description for each Z8 type is given in the following sections. Variations within each group are specified where applicable.

Product Part nr ROM I/O pins Dedicated I/O PCB footprint Comments
2K ROM Z8601 2K 32
4 ports
8 power/control 40 pin Masked ROM part, used primarily for high volume productions
2K Protopack Z8603 - 32
4 ports
8 power/control
40 pin Piggyback part, used for prototyping
4K ROM Z8611 4K 32
4 ports
8 power/control 40 pin Masked ROM part, used primarily for high volume productions
4K Development part Z8612 - 32
4 ports
8 power/control
24 external memory
64 pin ROMless part, used primarily in development systems
4K Protopack Z8613 - 32
4 ports
8 power/control
40 pin Piggyback part, used for prototyping
BASIC/Debug Z8671 2K 32
4 ports
8 power/control 40 pin BASIC/Debug part used in low volume applications
ROMless Z8681
2K 24
3 ports
8 power/control
8 external memory
40 pin Low cost ROMless production part with reduced I/O
Program memory is external

1.3 Microcomputers (Z8601 and Z8611).

The Z8 can be a stand-alone MCU with either 2 KB (Z8601) or 4 KB (Z8611) of internal ROM, a traditional CPU that can manage up to 124 KB (Z8601) or 120 KB of external memory, or a parallel processing element in a system with other processors and peripheral controllers linked by a Z-BUS. In all configurations, a large number of device pins are availbale for I/O. Key features of the Z8601 and Z8611 MCU include:

Pin functions and descriptions for the Z8601 and Z861 MCU can be found in chapter 6.

1.4 Development device (Z8612).

A development device allows users to prototype a system with an actual hardware device and to develop the code that is eventually mask-programmed into the on-chip ROM of the Z8601 or Z8611 MCU's. Development devices are also useful in applications where production volume does not justify the expense of a ROM system. The Z8612 development device is identical to its equivalent MCU, the Z8611, with the following exceptions:

Pin functions and descriptions for the development device can be found in the appendix.

1.5 Protopack emulators Z8603 and Z8613.

The protopack emulator devices are ROMless versions of their equivalent MCU's. The emulators differ from their development devices in two ways:

The emulator package allows for flexibility of application since it can be used in either prototype or final printed circuit boards, yet still allows for program development.
When the final program is developed it can be mask-programmed into the Z8601 or Z8611 which then replaces the emulator. The emulator is also useful in small volume applications where the cost of mask-programming is too high or where program flexibility is desired.

Physical description for the protopack emulator is found in the appendix

1.6 BASIC/Debug interpreter Z8671.

The Z8671 MCU is a complete microcomputer preprogrammed with a BASIC/Debug interpreter. BASIC/Debug can directly address the Z8671's internal registers and all external memory. It can quickly examine and modify any external memory location or I/O port and call machine language subroutines to increase execution speed.
The Z8671 MCU has a combination of software and hardware that is ideal for most industrial control applications. Along with the functions mentioned above, this microcomputer has a self contained line editor for interactive debugging which further speeds program development. In addition the BASIC/Debug interpreter allows program execution on power-up or reset, without operator intervention.

Two kinds of memory exist in the Z8671 device:

The BASIC/Debug interpreter is based in the on-chip 2 KB of ROM. Maximum addressing capability is 62 KB of external program memory and 62 KB of data memory. In addition, 32 I/O lines, a 144 byte register file, an onboard UART and two counter/timers are provided.

Pin descriptions and functions are the same as those for the Z8601 and Z8611 devices (chapter 6).

1.7 ROMless Microcomputers Z8681 and Z8682.

The Z8681 and Z8682 ROMless MCU's provide virtually all of the functions of the standard Z8 MCU without the need to mask-program on-chip ROM. This MCU is similar to the Z8601 version except that there is no internal program memory. Unlike the ROMless protopack and development devices, the Z8681 and Z8682 do not have additional address and datalines and it has no piggyback EPROM socket.
Use of external memory rather than internal ROM enables this Z8 device to be used in low volume applications or where code flexibility is required. The use of ports 0 and 1 to interface external memory leaves 16 to 24 lines of I/O.
Since port 1 is dedicated as an 8 bit multiplexed Address/Data bus, and port 0 lines can be programmed as address bits, the resulting 16 bit addresses can directly address 64 KB of memory for the Z8681 and 62 KB for the Z8682. The latter cannot address the lower 2 Kb of memory.
The address capability of the Z8681 and Z8682 can be doubled by programming output P34 as Data Memory (-DM) select signal. The two states of this signal can be used with the 16 bit addresses to identify two separate external address spaces for program and data memory. Thus increasing the address spaces to 128 KB for the Z8681 and 124 KB for the Z8682.

Pin functions and descriptions for the Z8681 and Z8682 MCU can be found in chapter 7.

1.8 Applications.

Z8 MCU's are most often used in high-performance dedicated applications. Such specialized functions were previously accomplished with TTL logic, TTL logic with a low-end MCU or a complete microprocessor plus peripherals. Some typical applications include:

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