LPC2458

• LPC2458 has two PWMs with the same operational features. These may be operated in a synchronized fashion by setting them both up to run at the same rate, then enabling both simultaneously. PWM0 acts as the master and PWM1 as the slave for this use.
• Counter or Timer operation (may use the peripheral clock or one of the capture inputs as the clock source).
• Seven match registers allow up to 6 single edge controlled or 3 double edge controlled PWM outputs, or a mix of both types. The match registers also allow:
Continuous operation with optional interrupt generation on match.
Stop timer on match with optional interrupt generation.
Reset timer on match with optional interrupt generation.
• Supports single edge controlled and/or double edge controlled PWM outputs. Single edge controlled PWM outputs all go high at the beginning of each cycle unless the output is a constant low. Double edge controlled PWM outputs can have either edge occur at any position within a cycle. This allows for both positive going and negative  going pulses.
• Pulse period and width can be any number of timer counts. This allows complete
flexibility in the trade-off between resolution and repetition rate. All PWM outputs will occur at the same repetition rate.
• Double edge controlled PWM outputs can be programmed to be either positive going or negative going pulses.
• Match register updates are synchronized with pulse outputs to prevent generation of erroneous pulses. Software must 'release' new match values before they can become effective.
• May be used as a standard timer if the PWM mode is not enabled.
• A 32-bit Timer/Counter with a programmable 32-bit Prescaler.

The LPC2458 microcontroller consists of an ARM7TDMI-S CPU with emulation support,
the ARM7 local bus for closely coupled, high-speed access to the majority of on-chip
memory, the AMBA AHB interfacing to high-speed on-chip peripherals and external
memory, and the AMBA APB for connection to other on-chip peripheral functions. The microcontroller permanently configures the ARM7TDMI-S processor for little-endian byte order.

The LPC2458 implements two AHB buses in order to allow the Ethernet block to operate without interference caused by other system activity. The primary AHB, referred to as AHB1, includes the VIC, GPDMA controller, and EMC.

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.