AMD manual Kbytes of memory, Am79C930 Device ISA Plug And Play Mode Memory Map

AMD		P R E L I M I N A R Y
Am79C930 Device ISA Plug And Play Mode Memory And I/O Resource Requirements
Memory Range	Memory Size		I/O Range	I/O Size
MBA*+0000h –	32 Kbytes		IOBA**+0000h – IOBA**+000Fh	16 bytes
MBA*+7FFFh	OR		and I/O 0279h and I/O 0A79h
	0 bytes		and I/O 0203h – I/O 03FFh (one byte only)

*MBA = ISA Plug and Play Memory Base Address **IOBA = ISA Plug and Play I/O Base Address

Note that since the Am79C930 device's memory mapped resources are all accessible through the Local Memory Address Register and I/O Data Ports (SIR2,3,4,5,6,7), it is possible to program the ISA Plug and Play Memory Base Address, and Memory upper limit Address or range length for descriptor 0, such that the Am79C930 device is assigned no memory space. (This is accomplished by assigning all 0s for both the Memory Base Address and the Memory range length value. The ISA Plug and Play utility can be instructed to make this selection through appropriate Resource Data programming.) By assigning no memory space to the Am79C930 device, the Am79C930 device will become an I/O only device. Such an arrangement may be con- venient for systems in which there is not enough total available memory space to allow the Am79C930 device to use a full 32K block of memory. Note that when this option is chosen, the total amount of bus bandwidth re- quired to perform all of the necessary accesses to the Am79C930-based system will be increased somewhat, because of the indirect nature of the I/O method of ac- cess to Am79C930-based resources.

The Am79C930 device requires the use of a single IRQ channel. Any of the following channels within an ISA Plug and Play system may be utilized by the Am79C930 device:

IRQ 4, 5, 9, 10, 11 or 12.

ISA Plug and Play Memory Resources — While the system memory space of the Am79C930 device only accommodates access to 32 Kbytes of memory, the Am79C930 device uses device select and bank select bits in SIR1 in order to access a total of 256K of memory space. Note that ISA accesses to memory locations 7C00h–7FFFh (1K total space) will sometimes correspond to the same physical locations as ISA ac- cesses to Plug and Play resource data locations 0000h–03FFh, i.e., the correspondence will occur only when the device and bank select bits of SIR1 are point- ing at the upper page of the 128K Flash memory ad- dress space. The following table indicates the mapping of the 256 Kbytes of physical memory space into the

32 Kbytes of memory:

Am79C930 Device ISA Plug And Play Mode Memory Map

ISA Address in Memory	SIR1[5:3]	Size of Space	Physical Memory
MBA+0000h – MBA+7FFFh	000	32 Kbytes	SRAM Memory 0	0000h	– 0 7FFFh
MBA+0000h – MBA+7FFFh	001	32 Kbytes	SRAM Memory 0	8000h	– 0 FFFFh
MBA+0000h – MBA+7FFFh	010	32 Kbytes	SRAM Memory 1	0000h	– 1 7FFFh
MBA+0000h – MBA+7FFFh	011	32 Kbytes	SRAM Memory 1 8000h – 1 FFFFh
MBA+0000h – MBA+7FFFh	100	32 Kbytes	Flash Memory 0 0000h – 0 7FFFh
MBA+0000h – MBA+7FFFh	101	32 Kbytes	Flash Memory 0 8000h – 0 FFFFh
MBA+0000h – MBA+7FFFh	110	32 Kbytes	Flash Memory 1 0000h – 1 7FFFh
MBA+0000h – MBA+7FFFh	111	32 Kbytes	Flash Memory 1 8000h – 1 FFFFh
	TOTAL:	256 Kbytes

*MBA = ISA Plug and Play Memory Base Address

When accessing Am79C930 memory resources through ISA memory cycle accesses, the upper 9 bits of the ISA memory address will be used to check for a match of the address range assigned to the Am79C930 device by the Plug and Play configuration program (i.e.,

the Memory Base Address = MBA, and Memory range length). The Plug and Play configuration program will have written a memory base address value into the Memory Base Address registers (Plug and Play ports 40h and 41h). The ISA Plug and Play memory base

64 Am79C930