NXP Semiconductors LPC24XX UM10237 - Manual (Page 9)

UM10237_4 © NXP B.V. 2009. All rights reserved.
User manual Rev. 04 — 26 August 2009 9 of 792
NXP Semiconductors
UM10237
Chapter 1: LPC24XX Introductory information
The second AHB, referred to as AHB2, includes only the Ethernet block and an
associated 16 kB SRAM. In addition, a bus bridge is provided that allows the secondary
AHB to be a bus master on AHB1, allowing expansion of Ethernet buffer space into
off-chip memory or unused space in memory residing on AHB1.
In summary, bus masters with access to AHB1 are the ARM7 itself, the GPDMA function,
and the Ethernet block (via the bus bridge from AHB2). Bus masters with access to AHB2
are the ARM7 and the Ethernet block.
AHB peripherals are allocated a 2 MB range of addresses at the very top of the 4 GB
ARM memory space. Each AHB peripheral is allocated a 16 kB address space within the
AHB address space. Lower speed peripheral functions are connected to the APB bus.
The AHB to APB bridge interfaces the APB bus to the AHB bus. APB peripherals are also
allocated a 2 MB range of addresses, beginning at the 3.5 GB address point. Each APB
peripheral is allocated a 16 kB address space within the APB address space.
The ARM7TDMI-S processor is a general purpose 32-bit microprocessor, which offers
high performance and very low power consumption. The ARM architecture is based on
Reduced Instruction Set Computer (RISC) principles, and the instruction set and related
decode mechanism are much simpler than those of microprogrammed complex
instruction set computers. This simplicity results in a high instruction throughput and
impressive real-time interrupt response from a small and cost-effective processor core.
Pipeline techniques are employed so that all parts of the processing and memory systems
can operate continuously. Typically, while one instruction is being executed, its successor
is being decoded, and a third instruction is being fetched from memory.
The ARM7TDMI-S processor also employs a unique architectural strategy known as
Thumb, which makes it ideally suited to high-volume applications with memory
restrictions, or applications where code density is an issue.
The key idea behind Thumb is that of a super-reduced instruction set. Essentially, the
ARM7TDMI-S processor has two instruction sets:
• the standard 32-bit ARM set
• a 16-bit Thumb set
The Thumb set’s 16-bit instruction length allows it to approach higher density compared to
standard ARM code while retaining most of the ARM’s performance.
7. On-chip flash programming memory (LPC2458/68/78)
The LPC2400 incorporates 512 kB Flash memory system. This memory may be used for
both code and data storage. Programming of the Flash memory may be accomplished in
several ways. It may be programmed In System via the serial port (UART0). The
application program may also erase and/or program the Flash while the application is
running, allowing a great degree of flexibility for data storage field and firmware upgrades.
The Flash memory is 128 bits wide and includes pre-fetching and buffering techniques to
allow it to operate at speeds of 72 MHz.
The LPC2400 provides a minimum of 100000 write/erase cycles and 20 years of data
retention.