W89C926 Datasheet, PDF (23/48 Pages) Winbond – PCMCIA ETHERNET NETWORK TWISTED PAIR INTERFACE CONTROLLER

W89C926 PENTIC+
out before the buffer ring overflows. This is done through a remote DMA read operation, which is
simply a "IN" command on the PC.
SHARED MEMORY MODE OPERATION
In this mode, the local memory is mapped as part of the system memory. When it requires data
transmission, the host fills the transmit buffer SRAM by a memory move operation and then issues a
transmit command to the PENTIC+. When it receives data, the PENTIC+ will generate an interrupt
to the host by asserting IREQ when one or more packets have been received. The PENTIC+ will then
place the packets into the shared memory. The host should check the shared memory and remove
the data before the buffer ring overflows.
Bus arbitration is performed between the host and LCE core for shared memory usage. When
memory accesses are issued, the arbiter will grant the bus master an acknowledge signal, which is a
BACK to the LCE or a WAIT signal to the host. There is no predefined priority in the PENTIC+; bus
arbitration is performed on a first-come, first-served basis.
To implement the shared memory mode, the PENTIC+ uses memory mapping register A (MMA) and
memory mapping register B (MMB) for memory mapping control. Since the PENTIC+ will operate in
16-bit shared memory operation at shared memory base address 00000H only, 0s should be written
to MMB and bit 0 to 5 of MMA. The contents of the MMA are described below.
MMA (Memory Mapping Register A)
MMA is used for memory enable and software reset. It is located in I/O space, 00H, and can be ac-
cessed only in shared memory mode.
Access Address: IOBASE + 00H
Access Type: write-only
BIT
SYMBOL
0-5
-
6
MEN
7
SRESET
DESCRIPTION
Reserved. Should be set to 0.
If this bit is high, the buffer memory may be accessed by the
system; if it is low, the buffer memory access is disabled. This
bit is 0 at power-on.
A shared memory mode software reset is issued when a 1 is
written to this bit. Writing a 0 to this bit will clear the software
reset. This bit is 0 at power-on.
AUTO MEDIA-SWITCHING FUNCTION
The PENTIC+ also provides a user-friendly auto media-switching function. If the PENTIC+ is
configured at the TPI, link checking is enabled, and the UTP link is broken, the PENTIC+ will detect
the link status and switch to the BNC port immediately. After the UTP link is repaired, the PENTIC+
will detect the good link and switch back to the TPI again.
If, however, the PENTIC+ is not configured at the TPI or link checking is disabled, the auto media-
switching function will be disabled.
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Publication Release Date: January 1996
Revision A1