W89C926 Datasheet, PDF (25/48 Pages) Winbond – PCMCIA ETHERNET NETWORK TWISTED PAIR INTERFACE CONTROLLER

W89C926 PENTIC+
Core Register Files
The register files of the SLCT can be accessed by means of IO commands. The PENTIC+ should be
in slave mode when the system accesses the register files. The command register (CR) determines
the page number of the register file, while the system address HA<0:4> selects one register address
from 01H to 0FH (I/O mode) or from 10H to 1FH (shared memory mode). The PCMCIA IORD and
IOWR are the read/write commands used to activate the I/O operations. Refer to the W89C90 data
sheet for more detailed information on the registers.
DMA Interface Logic
In I/O mapping mode, the SLCT provides two types of DMA operations, local DMA and remote DMA.
In shared memory mode, only local DMA is available.
Local DMA
The local DMA transfers data from/to the on-board buffers. To perform data reception or transmission
from/to remote nodes in the network, data must be moved from/to the FIFO. To enhance the effi-
ciency of the transmission, the local DMA transfers data in batches: data are first collected and then
moved in a batch. Up to 12 bytes of data can be moved in each transfer. This scheme reduces time
wasted in requesting the bus.
A local DMA begins by requesting the local bus. If the local bus is available to the SLCT core, the bus
arbiter inside the PENTIC+ responds at once by asserting the bus acknowledge (BACK, refer to
LCE); if, on the other hand, the bus is currently authorized to another device, the arbiter will not assert
the bus acknowledge and the SLCT must wait. Note that this sequence will not affect the host system
or system bus signals. After each batch of data is transferred, the SLCT checks the FIFO threshold
levels to determine if another batch transfer should be requested.
Remote DMA
A remote DMA can be performed only in I/O mode. The remote DMA moves data between the host
and the local buffers. Unlike a local DMA, the remote DMA is word-wide: the remote DMA operation
transfers one word each time.
Since a remote DMA is simply a system I/O operation, it sometimes affects the system bus. If the
remote DMA is interleaved with other devices, WAIT is asserted to force the system to insert wait
states. The PENTIC+ will automatically handle any arbitration necessary.
- 25 -
Publication Release Date: January 1996
Revision A1