C8051F040/1/2/3/4/5/6/7
232 Rev. 1.5
18.2.3. Message Handler Registers
The Message Handler Registers are read only registers. Their flags can be read via the indexed access
method with CAN0ADR, CAN0DATH, and CAN0DATL. The message handler registers provide interrupt,
error, transmit/receive requests, and new data information.
Please refer to the Bosch CAN User’s Guide for information on the function and use of the Message Han-
dler Registers.
18.2.4. CIP-51 MCU Special Function Registers
C8051F04x family peripherals are modified, monitored, and controlled using Special Function Registers
(SFR’s). Only three of the CAN Controller’s registers may be accessed directly with SFR’s. However, all
CAN Controller registers can be accessed indirectly using three CIP-51 MCU SFR’s: the CAN Data Regis-
ters (CAN0DATH and CAN0DATL) and CAN Address Register (CAN0ADR).
18.2.5. Using CAN0ADR, CAN0DATH, and CANDATL to Access CAN Registers
Each CAN Controller Register has an index number (see Table 18.2). The CAN register address space is
128 words (256 bytes). A CAN register is accessed via the CAN Data Registers (CAN0DATH and
CAN0DATL) when a CAN register’s index number is placed into the CAN Address Register (CAN0ADR).
For example, if the Bit Timing Register is to be configured with a new value, CAN0ADR is loaded with
0x03. The low byte of the desired value is accessed using CAN0DATL and the high byte of the bit timing
register is accessed using CAN0DATH. CAN0DATL is bit addressable for convenience. To load the value
0x2304 into the Bit Timing Register:
CAN0ADR = 0x03; // Load Bit Timing Register’s index (Table 18.1)
CAN0DATH = 0x23; // Move the upper byte into data reg high byte
CAN0DATL = 0x04; // Move the lower byte into data reg low byte
Note: CAN0CN, CAN0STA, and CAN0TST may be accessed either by using the index method, or by direct
access with the CIP-51 MCU SFR’s. CAN0CN is located at SFR location 0xF8/SFR page 1 (SFR Definition
18.3), CAN0TST at 0xDB/SFR page 1 (SFR Definition 18.4), and CAN0STA at 0xC0/SFR page 1 (SFR
Definition 18.5).
18.2.6. CAN0ADR Autoincrement Feature
For ease of programming message objects, CAN0ADR features autoincrementing for the index ranges
0x08 to 0x12 (Interface Registers 1) and 0x20 to 0x2A (Interface Registers 2). When the CAN0ADR regis-
ter has an index in these ranges, the CAN0ADR will autoincrement by 1 to point to the next CAN reg-
ister 16-bit word upon a read/write of CAN0DATL
. This speeds programming of the frequently-
accessed interface registers when configuring message objects.
NOTE:
Table 18.2 below supersedes Figure 5 in Section 3, “Programmer’s Model” of the Bosch CAN
User’s Guide.
