LPC2921 datasheet(29/81 Pages) PHILIPS

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LPC2921_2923_2925_0

Preliminary data sheet

Rev. 00.01 — 24 October 2008

29 of 81

NXP Semiconductors

LPC2921/2923/2925

ARM9 microcontroller with CAN and LIN

6.12.6.3

Clock description

The GPIO modules are clocked by several clocks, all of which are derived from

BASE_SYS_CLK; CLK_SYS_PESS and CLK_SYS_GPIOx (x = 0, 1, 5), see

Section 6.7.2. Note that each GPIO has its own CLK__SYS_GPIOx branch clock for

power management. The frequency of all clocks CLK_SYS_GPIOx is identical to

CLK_SYS_PESS since they are derived from the same base clock BASE_SYS_CLK.

6.13 Networking subsystem

6.13.1 CAN gateway

Controller Area Network (CAN) is the definition of a high-performance communication

protocol for serial data communication. The two CAN controllers in the

LPC2921/2923/2925 provide a full implementation of the CAN protocol according to the

CAN specification version 2.0B. The gateway concept is fully scalable with the number of

CAN controllers, and always operates together with a separate powerful and flexible

hardware acceptance filter.

The key features are:

• Supports 11-bit as well as 29-bit identifiers

• Double receive buffer and triple transmit buffer

• Programmable error-warning limit and error counters with read/write access

• Arbitration-lost capture and error-code capture with detailed bit position

• Single-shot transmission (i.e. no re-transmission)

• Listen-only mode (no acknowledge; no active error flags)

• Reception of ‘own’ messages (self-reception request)

• Full CAN mode for message reception

6.13.1.1

Global acceptance filter

The global acceptance filter provides look-up of received identifiers - called acceptance

filtering in CAN terminology - for all the CAN controllers. It includes a CAN ID look-up table

memory, in which software maintains one to five sections of identifiers. The CAN ID

look-up table memory is 2 kB large (512 words, each of 32 bits). It can contain up to 1024

standard frame identifiers or 512 extended frame identifiers or a mixture of both types. It is

also possible to define identifier groups for standard and extended message formats.

6.13.1.2

Pin description

The two CAN controllers in the LPC2921/2923/2925 have the pins listed below. The CAN

pins are combined with other functions on the port pins of the LPC2921/2923/2925.

Table 17 shows the CAN pins (x runs from 0 to 1).

Table 17.

CAN pins

Symbol

Pin name

Direction

Description

CANx TXD

TXDC0/1

OUT

CAN channel x transmit data output

CANx RXD

RXDC0/1

CAN channel x receive data input

LPC2921 Datasheet(PDF) 29 Page - NXP Semiconductors

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