Z8 CPU Product Overview
The ZiLOG Z8 microcontroller (MCU) product line continues to expand with new product introductions. ZiLOG MCU products are targeted for cost-sensitive, high-volume applications including consumer, automotive, security, and HVAC. It includes ROM-based products geared for high volume production (where software is stable) and one-time programmable (OTP) equivalents for prototyping as well as volume production where time to market or code flexibility is critical (see Table 1 on page 4). A variety of packaging options are available including plastic DIP, SOIC, PLCC, and QFP.
A generalized Z8 CPU® block diagram is shown in Figure 1. The same on-chip peripherals are used across the MCU product line with the primary differences being the amount of ROM/RAM, number of I/O lines present, and packaging/temperature ranges available. This allows code written for one MCU device to be easily ported to another family member.

Key Features
General-Purpose Register File. Every RAM register acts like an accumulator, speeding instruction execution and maximizing coding efficiency. Working register groups allow fast context switching.

Flexible I/O. I/O byte, nibble, and/or bit programmable as inputs or outputs. Outputs are software programmable as open-drain or push–pull on a port basis. Inputs are Schmitt-triggered with autolatches to hold unused inputs at a known voltage state.

Analog Inputs. Three input pins are software programmable as digital or analog inputs. When in analog mode, two comparator inputs are provided with a common reference input. These inputs are ideal for a variety of common functions, including threshold level detection, analog-to-digital conversion, and short circuit detection. Each analog input provides a unique maskable interrupt input.

Timer/Counter. The Timer/Counter (T/C) consists of a programmable 6-bit prescaler and 8-bit downcounter, with maskable interrupt upon end-of-count. Software controls T/C load/start/stop, countdown read (at any time on the fly), and maskable end-of-count interrupt. Special functions available include TIN (external counter input, external gate input, or external trigger input) and TOUT (external access to timer output or the internal system clock.) These special functions allow accurate hardware input pulse measurement and output waveform generation.

Interrupts. There are six vectored interrupt sources with software-programmable enable and priority for each of the six sources.

Watch–Dog Timer. An internal Watch–Dog Timer (WDT) circuit is included as a fail-safe mechanism so that if software strays outside the bounds of normal operation, the WDT will time-out and reset the MCU. To maximize circuit robustness and reliability, the default WDT clock source is an internal RC circuit (isolated from the device clock source).

Auto Reset/Low-Voltage Protection. All family devices have internal Power-On Reset. ROM devices add low-voltage protection. Low-voltage protection ensures the MCU is in a known state at all times (in active RUN mode or RESET) without external hardware (or a device reset pin).

Low-EMI Operation. Mode is programmable via software or as a mask option. This new option provides for reduced radiated emission via clock and output drive circuit changes.

Low-Power. CMOS with two standby modes; STOP and HALT.

Full Z8 Instruction Set. Forty-eight basic instructions, supported by six addressing modes with the ability to operate on bits, nibbles, bytes, and
words.