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Am79C930
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