Z86C30 datasheet(28/348 Pages) ZILOG

28 / 348 page

Z8 Family of Microcontrollers

User Manual

Address Space

UM001602-0904

When instructions are executed, registers are read when deﬁned as

sources and written when deﬁned as destinations. All General-Purpose

Registers function as accumulators, address pointers, index registers,

stack areas, or scratch pad memory.

General-Purpose Registers

General-Purpose Registers (GPR) are undeﬁned after the device is pow-

ered up. The registers keep their last value after any reset, as long as the

reset occurs in the VCC voltage-speciﬁed operating range. It will not keep

its last state from a VLV reset if VCC drops below 1.8v.

Registers in Bank E0-EF may only be accessed through the working regis-

ter and indirect addressing modes. Direct access cannot be used because

the 4-bit working register address mode already uses the format [E | dst],

where dst represents the working register number from 0h to Fh.

RAM Protect

The upper portion of the register ﬁle address space 80h to EFh (excluding

the control registers) may be protected from reading and writing. The

RAM Protect bit option is mask-programmable and is selected by the cus-

tomer when the ROM code is submitted. After the mask option is

selected, the user activates this feature from the internal ROM code to

turn off/on the RAM Protect by loading either a 0 or 1 into the IMR regis-

ter, bit D6. A 1 in D6 enables RAM Protect. Only devices that use regis-

ters 80h to EFh offer this feature.

Working Register Groups

Z8 instructions can access 8-bit registers and register pairs (16-bit words)

using either 4-bit or 8-bit address ﬁelds. 8-bit address ﬁelds refer to the

actual address of the register. For example, Register 58h is accessed by

calling upon its 8-bit binary equivalent, 01011000 (58h).

With 4-bit addressing, the register ﬁle is logically divided into 16 Work-

ing Register Groups of 16 registers each, as shown in Table 3. These 16

Note:

Z86C30 Datasheet(PDF) 28 Page - Zilog, Inc.