MC68376BGMAB20 Freescale Semiconductor, MC68376BGMAB20 Datasheet - Page 262

• Manufacturer Part Number: MC68376BGMAB20
• Description: IC MCU 32BIT 8K ROM 160-QFP
• Manufacturer: Freescale Semiconductor
• Series: M683xxr

Specifications of MC68376BGMAB20

• Core Processor: CPU32
• Core Size: 32-Bit
• Speed: 20MHz
• Connectivity: CAN, EBI/EMI, SCI, SPI
• Peripherals: POR, PWM, WDT
• Number Of I /o: 18
• Program Memory Type: ROMless
• Ram Size: 7.5K x 8
• Voltage - Supply (vcc/vdd): 4.75 V ~ 5.25 V
• Data Converters: A/D 16x10b
• Oscillator Type: External
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 160-QFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Program Memory Size: -

13.4.1.4 Serial Message Buffers
13.4.1.5 Message Buffer Activation/Deactivation Mechanism
13.4.1.6 Message Buffer Lock/Release/Busy Mechanism
13-6
MOTOROLA
RTR/SRR Bit
16-Bit Time
To allow double buffering of messages, the TouCAN has two shadow buffers called
serial message buffers. These two buffers are used by the TouCAN for buffering both
received messages and messages to be transmitted. Only one serial message buffer
is active at a time, and its function depends upon the operation of the TouCAN at that
time. At no time does the user have access to or visibility of these two buffers.
Each message buffer must be activated once it is configured for the desired operation
by the user. A buffer is activated by writing the appropriate code to the control/status
word for that buffer. Once the buffer is activated, it will begin participating in the normal
transmit and receive processes.
Likewise, a buffer is deactivated by writing the appropriate deactivation code to the
control/status word for that buffer. Deactivation of a buffer is typically done when the
user desires to reconfigure the buffer, for example to change the buffer’s function (RX
to TX or TX to RX). Deactivation should also be done before changing a receive buff-
er’s message identifier or before loading a new message to be transmitted into a trans-
mit buffer.
For more details on activation and deactivation of message buffers, and the effects on
message buffer operation, refer to 13.5 TouCAN Operation.
In addition to the activation/deactivation mechanism, the TouCAN also utilizes a lock/
release/busy mechanism to assure data coherency during the receive process. The
mechanism includes a lock status for each message buffer, and utilizes the two serial
message buffers to facilitate frame transfers within the TouCAN.
Reading the control/status word of a receive message buffer triggers the lock for that
buffer. While locked, a received message cannot be transferred into that buffer from
one of the SMBs.
Treatment
ID[28:18]
Stamp
Field
RTR
The ID LOW word, which is not needed for standard format, is used in a standard format buffer
to store the 16-bit value of the free-running timer which is captured at the beginning of the iden-
tifier field of the frame on the CAN bus.
Contains bits [28:18] of the identifier, located in the ID HIGH word of the message buffer. The four
least significant bits in this register (corresponding to the IDE bit and ID[17:15] for an extended
identifier message) must all be written as logic zeros to ensure proper operation of the TouCAN.
This bit is located in the ID HIGH word of the message buffer;
0 = data frame, 1 = remote frame.
If the TouCAN transmits this bit as a one and receives it as a zero, an “arbitration loss” is indicat-
ed. If the TouCAN transmits this bit as a zero and is receives it as a one, a bit error is indicated.
If the TouCAN transmits a value and receives a matching response, a successful bit transmission
is indicated.
CAN 2.0B CONTROLLER MODULE (TouCAN)
Table 13-5 Standard Format Frames
Description
USER’S MANUAL
MC68336/376