Intel Microcontroller, 80C196NU, 8XC196NP Base Addresses for Several Sizes of the Address Range

INTERFACING WITH EXTERNAL MEMORY

Observe the following restrictions in choosing an address range for a chip-select output:

•The addresses in the address range must be contiguous.

•The size of the address range must be 2n bytes, where n = 8, 9, ..., 20. This corresponds to block sizes of 256 bytes, 512 bytes, ..., 1 Mbyte.

•The base address of a 2n-byte address range must be on a 2n-byte boundary (that is, the base address must be evenly divisible by 2n). For example, the base address of a 256-Kbyte range must be 00000H, 40000H, 80000H, or C0000H. Table 13-6 shows the base addresses for some address-range sizes.

•The address ranges for different chip-selects must not overlap, unless their BUSCONx parameters (wait states, bus width, and multiplexing) have the same values. If BUSCONx registers have different parameter values and an address in their overlapping region is accessed, the results are unpredictable. See “Example of a Chip-select Setup” on page 13-12 for a chip-select initialization procedure that avoids this difficulty.

Table 13-6. Base Addresses for Several Sizes of the Address Range

Address-	1 Mbyte	512 Kbyte	256 Kbyte		512 bytes	256 bytes
Range Size
	00000H	00000H	00000H		00000H	00000H
		80000H	40000H		00200H	00100H
			80000H	• • •	00400H	00200H
Base
			C0000H		00600H	00300H
Addresses
					• • •	• • •
					FFB00H	FFE00H
					FFD00H	FFF00H

For an address range satisfying these restrictions, set up the ADDRCOMx and ADDRMSKx reg- isters as follows:

•Place the 12 most-significant bits of the base address into bits BASE19:8 in the ADDRCOMx register (Figure 13-2).

•For an address range of 2n bytes, set the n1 most-significant bits of MASK19:8 in the ADDRMSKx register (Figure 13-3), where n1 = 20 – n.

For example, assume that chip-select output x is to be assigned to a 32-Kbyte address range with base address E0000H. The address range size is 32 × 1024 = 215, and n1 = 20 –15 = 5. To set up the registers, write the 12 most-significant bits of E0000H to BASE19:8 in the ADDRCOMx reg- ister, and set the 5 most-significant bits of MASK19:8 in the ADDRMSKx register:

ADDRCOMx = 0E00H

ADDRMSKx = 0F80H

13-9