SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 11

• Manufacturer Part Number: SAB80C517-M16
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Fundamental Structure
Central Processing Unit
The CPU is designed to operate on bits and bytes. The instructions, which consist of up to 3 bytes,
are performed in one, two or four machine cycles. One machine cycle requires twelve oscillator
cycles. The instruction set has extensive facilities for data transfer, logic and arithmetic instructions.
The Boolean processor has its own full-featured and bit-based instructions within the instruction set.
The SAB 80C517 uses five addressing modes: direct access, immediate, register, register indirect
access, and for accessing the external data or program memory portions a base register plus index-
register indirect addressing.
Memory Organization
The SAB 80C517 has an internal ROM of 8 Kbyte. The program memory can externally be
expanded up to 64 Kbyte (see Bus Expansion Control). The internal RAM consists of 256 bytes.
Within this address space there are 128 bit-addressable locations and four register banks, each
with 8 general purpose registers. In addition to the internal RAM there is a further 128-byte address
space for the special function registers, which are described in sections to follow.
Because of its Harvard architecture, the SAB 80C517 distinguishes between an external program
memory portion (as mentioned above) and up to 64 Kbyte external data memory accessed by a set
of special instructions. As an important improvement of the 8051 architecture, the SAB 80C517
contains eight datapointers (instead of one in the 8051) which speed up external data access.
Bus Expansion Control
The external bus interface of the SAB 80C517 consists of an 8-bit data bus (port 0), a 16-bit address
bus (port 0 and port 2) and five control lines. The address latch enable signal (ALE) is used to
demultiplex address and data of port 0. The program memory is accessed by the program store
enable signal (PSEN) twice a machine cycle. A separate external access line (EA) is used to inform
the controller while executing out of the lower 8 Kbyte of the program memory, whether to operate
out of the internal or external program memory. The read or write strobe (RD, WR) is used for
accessing the external data memory.
Peripheral Control
All on-chip peripheral components - I/O ports, serial interfaces, timers, compare/capture registers,
the interrupt controller and the A/D converter - are handled and controlled by the so-called special
function registers. These registers constitute the easy-to-handle interface with the peripherals. This
peripheral control concept, as implemented in the SAB 8051, provides the high flexibility for further
expansion as done in the SAB 80C517.
Moreover some of the special function registers, like accumulator, Bregister, program status word
(PSW), stack pointer (SP) and the data pointers (DPTR) are used by the CPU and maintain the
machine status.
Semiconductor Group
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