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| 型号： | MCP2510-E/SOG |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 1 CHANNEL(S), 1M bps, LOCAL AREA NETWORK CONTROLLER, PDSO18 |
| 封装： | 0.300 INCH, PLASTIC, SOIC-18 |
| 文件页数： | 7/80页 |
| 文件大小： | 998K |
| 代理商： | MCP2510-E/SOG |
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2007 Microchip Technology Inc.
DS21291F-page 15
MCP2510
3.0
MESSAGE TRANSMISSION
3.1
Transmit Buffers
The MCP2510 implements three Transmit Buffers.
Each of these buffers occupies 14 bytes of SRAM and
are mapped into the device memory maps. The first
byte, TXBNCTRL, is a control register associated with
the message buffer. The information in this register
determines the conditions under which the message
will be transmitted and indicates the status of the mes-
sage transmission. (see Register 3-2). Five bytes are
used to hold the standard and extended identifiers and
other message arbitration information (see Register 3-
3 through Register 3-8). The last eight bytes are for the
eight possible data bytes of the message to be trans-
mitted (see Register 3-8).
For the MCU to have write access to the message
buffer, the TXBNCTRL.TXREQ bit must be clear, indi-
cating that the message buffer is clear of any pending
message to be transmitted. At a minimum, the TXBN-
SIDH, TXBNSIDL, and TXBNDLC registers must be
loaded. If data bytes are present in the message, the
TXBNDm registers must also be loaded. If the message
is to use extended identifiers, the TXBNEIDm registers
must also be loaded and the TXBNSIDL.EXIDE bit set.
Prior to sending the message, the MCU must initialize
the CANINTE.TXINE bit to enable or disable the gener-
ation of an interrupt when the message is sent. The
MCU must also initialize the TXBNCTRL.TXP priority
bits (see Section 3.2).
3.2
Transmit Priority
Transmit priority is a prioritization, within the MCP2510,
of the pending transmittable messages. This is inde-
pendent from, and not necessarily related to, any prior-
itization implicit in the message arbitration scheme built
into the CAN protocol. Prior to sending the SOF, the pri-
ority of all buffers that are queued for transmission is
compared. The transmit buffer with the highest priority
will be sent first. For example, if transmit buffer 0 has a
higher priority setting than transmit buffer 1, buffer 0 will
be sent first. If two buffers have the same priority set-
ting, the buffer with the highest buffer number will be
sent first. For example, if transmit buffer 1 has the same
priority setting as transmit buffer 0, buffer 1 will be sent
first. There are four levels of transmit priority. If TXBNC-
TRL.TXP<1:0> for a particular message buffer is set to
11, that buffer has the highest possible priority. If
TXBNCTRL.TXP<1:0> for a particular message buffer
is 00, that buffer has the lowest possible priority.
3.3
Initiating Transmission
To
initiate
message
transmission
the
TXBNC-
TRL.TXREQ bit must be set for each buffer to be trans-
mitted. This can be done by writing to the register via
the SPI interface or by setting the TXNRTS pin low for
the particular transmit buffer(s) that are to be transmit-
ted. If transmission is initiated via the SPI interface, the
TXREQ bit can be set at the same time as the TXP pri-
ority bits.
When
TXBNCTRL.TXREQ
is
set,
the
TXBNCTRL.ABTF,
TXBNCTRL.MLOA
and
TXBNCTRL.TXERR bits will be cleared.
Setting the TXBNCTRL.TXREQ bit does not initiate a
message transmission, it merely flags a message
buffer as ready for transmission. Transmission will start
when the device detects that the bus is available. The
device will then begin transmission of the highest prior-
ity message that is ready.
When the transmission has completed successfully the
TXBNCTRL.TXREQ bit will be cleared, the CAN-
INTF.TXNIF bit will be set, and an interrupt will be gen-
erated if the CANINTE.TXNIE bit is set.
If the message transmission fails, the TXBNC-
TRL.TXREQ will remain set indicating that the mes-
sage is still pending for transmission and one of the
following condition flags will be set. If the message
started to transmit but encountered an error condition,
the TXBNCTRL. TXERR and the CANINTF.MERRF
bits will be set and an interrupt will be generated on the
INT pin if the CANINTE.MERRE bit is set. If the mes-
sage lost arbitration the TXBNCTRL.MLOA bit will be
set.
3.4
TXnRTS Pins
The TXNRTS Pins are input pins that can be configured
as request-to-send inputs, which provides a secondary
means of initiating the transmission of a message from
any of the transmit buffers, or as standard digital inputs.
Configuration and control of these pins is accomplished
using the TXRTSCTRL register (see Register 3-2). The
TXRTSCTRL register can only be modified when the
MCP2510 is in configuration mode (see Section 9.0). If
configured to operate as a request to send pin, the pin
is mapped into the respective TXBNCTRL.TXREQ bit
for the transmit buffer. The TXREQ bit is latched by the
falling edge of the TXNRTS pin. The TXNRTS pins are
designed to allow them to be tied directly to the RXNBF
pins to automatically initiate a message transmission
when the RXNBF pin goes low. The TXNRTS pins have
internal pullup resistors of 100 k
Ω (nominal).
3.5
Aborting Transmission
The MCU can request to abort a message in a specific
message buffer by clearing the associated TXBnC-
TRL.TXREQ bit. Also, all pending messages can be
requested to be aborted by setting the CAN-
CTRL.ABAT bit. If the CANCTRL.ABAT bit is set to
abort all pending messages, the user MUST reset this
bit (typically after the user verifies that all TXREQ bits
have been cleared) to continue trasmit messages. The
CANCTRL.ABTF flag will only be set if the abort was
requested via the CANCTRL.ABAT bit. Aborting a mes-
sage by resetting the TXREQ bit does cause the ATBF
bit to be set.
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相关代理商/技术参数 |
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|---|---|
| MCP2510-EST | 制造商:MICROCHIP 制造商全称:Microchip Technology 功能描述:Stand-Alone CAN Controller with SPI Interface |
| MCP2510-I/P | 功能描述:网络控制器与处理器 IC Stand-alone CAN RoHS:否 制造商:Micrel 产品:Controller Area Network (CAN) 收发器数量: 数据速率: 电源电流（最大值）:595 mA 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:PBGA-400 封装:Tray |
| MCP2510-I/P | 制造商:Microchip Technology Inc 功能描述:IC CAN CONTROLLER 2510 DIP18 |
| MCP2510-I/SO | 功能描述:网络控制器与处理器 IC Stand-alone CAN RoHS:否 制造商:Micrel 产品:Controller Area Network (CAN) 收发器数量: 数据速率: 电源电流（最大值）:595 mA 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:PBGA-400 封装:Tray |
| MCP2510-I/SO | 制造商:Microchip Technology Inc 功能描述:IC CAN CONTROLLER 2510 SOIC18 |
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