Cirrus Logic CS8900A - Manual (Page 13)

DS271F5 13
CS8900A
Crystal LAN™ Ethernet Controller
CIRRUS LOGIC PRODUCT DATASHEET
ISA Bus Interface
SA[0:19] - System Address Bus, Input PINS 37-48, 50-54, 58-60.
Lower 20 bits of the 24-bit System Address Bus used to decode accesses to CS8900A
I/O and Memory space, and attached Boot PROM. SA0-SA15 are used for I/O Read
and Write operations. SA0-SA19 are used in conjunction with external decode logic for
Memory Read and Write operations.
SD[0:15] - System Data Bus, Bi-Directional with 3-State Output PINS 65-68, 71-74, 27-
24, 21-18.
Bi-directional 16-bit System Data Bus used to transfer data between the CS8900A and
the host.
RESET - Reset, Input PIN 75.
Active-high asynchronous input used to reset the CS8900A. Must be stable for at least
400 ns before the CS8900A recognizes the signal as a valid reset.
AEN - Address Enable, Input PIN 63.
When TEST is high, this active-high input indicates to the CS8900A that the system
DMA controller has control of the ISA bus. When AEN is high, the CS8900A will not
perform slave I/O space operations. When TEST is low, this pin becomes the shift
clock input for the Boundary Scan Test. AEN should be inactive when performing an
IO or memory access and it should be active during a DMA cycle.
MEMR - Memory Read, Input PIN 29.
Active-low input indicates that the host is executing a Memory Read operation.
MEMW - Memory Write, Input PIN 28.
Active-low input indicates that the host is executing a Memory Write operation.
MEMCS16 - Memory Chip Select 16-bit, Open Drain Output PIN 34.
Open-drain, active-low output generated by the CS8900A when it recognizes an
address on the ISA bus that corresponds to its assigned Memory space (CS8900A
must be in Memory Mode with the MemoryE bit (Register 17, BusCTL, Bit A) set for
MEMCS16 to go active). 3-Stated when not active.
REFRESH - Refresh, Input PIN 49.
Active-low input indicates to the CS8900A that a DRAM refresh cycle is in progress.
When REFRESH is low, MEMR, MEMW, IOR, IOW, DMACK0, DMACK1, and
DMACK2 are ignored.
IOR - I/O Read, Input PIN 61.
When IOR is low and a valid address is detected, the CS8900A outputs the contents
of the selected 16-bit I/O register onto the System Data Bus. IOR is ignored if
REFRESH is low.