Intel 87C196CB, 8XC196NT user manual Address Map, Message Objects

CAN SERIAL COMMUNICATIONS CONTROLLER

7.3.1Address Map

The CAN controller has 256 bytes of RAM, containing 15 message objects and control and status registers at fixed addresses. Each message object occupies 15 consecutive bytes beginning at a base address that is a multiple of 16 bytes. The byte above each message object is reserved (indi- cated by a dash (—) character) or occupied by a control register. The lowest 16 bytes of RAM contain the remaining control and status registers (Table 7-3). This 256-byte section of memory can be windowed for register-direct access.

Table 7-3. CAN Controller Address Map

Hex Address	Description
1EFF	—
1EF0–1EFE	Message Object 15
1EEF	—
1EE0–1EEE	Message Object 14
1EDF	—
1ED0–1EDE	Message Object 13
1ECF	—
1EC0–1ECE	Message Object 12
1EBF	—
1EB0–1EBE	Message Object 11
1EAF	—
1EA0–1EAE	Message Object 10
1E9F	—
1E90–1E9E	Message Object 9
1E8F	—
1E80–1E8E	Message Object 8
1E7F	—
1E70–1E7E	Message Object 7

Hex Address	Description
1E6F	—
1E60–1E6E	Message Object 6
1E5F	Interrupt Register
1E50–1E5E	Message Object 5
1E4F	Bit Timing Register 1 †
1E40–1E4E	Message Object 4
1E3F	Bit Timing Register 0 †
1E30–1E3E	Message Object 3
1E2F	—
1E20–1E2E	Message Object 2
1E1F	—
1E10–1E1E	Message Object 1
1E0C–1E0F	Message 15 Mask Register
1E08–1E0B	Extended Global Mask Register
1E06–1E07	Standard Global Mask Register
1E02–1E05	—
1E01	Status Register
1E00	Control Register†

†The control register’s CCE bit must be set to enable write access to the bit timing registers.

7.3.2Message Objects

The CAN controller includes 15 message objects, each of which occupies 15 bytes of RAM (Ta- ble 7-4). Message objects 1–14 can be configured to either transmit or receive messages, while message object 15 can only receive messages. Message objects 1–14 have only a single buffer, so if a second message is received before the CPU reads the first, the first message is overwritten. Message object 15 has two alternating buffers, so it can receive a second message while the first is being processed. However, if a third message is received while the CPU is reading the first, the second message is overwritten.

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