AM79C90 Advanced Micro Devices, AM79C90 Datasheet - Page 15

• Manufacturer Part Number: AM79C90
• Description: CMOS Local Area Network Controller for Ethernet (C-LANCE)
• Manufacturer: Advanced Micro Devices

Read Sequence (Master Mode)
A read cycle is begun by placing a valid address on
DAL00 – DAL15 and A16 – A23. The BYTE MASK sig-
nals are asserted to indicate a word, upper byte or lower
byte memory reference. READ indicates the type of cy-
cle. ALE or AS is pulsed, and the trailing edge of either
can be used to latch addresses. DAL00 – DAL15 go into
a 3-state mode, and DAS falls LOW to signal the begin-
ning of the memory access. The memory responds by
placing READY LOW to indicate that the DAL lines have
valid data. The C-LANCE then latches memory data on
the rising edge of DAS, which in turn ends the memory
cycle and READY returns HIGH. Refer to Figure 5-1.
DAL0–DAL15
(Output from
C-LANCE)
READY
READ
HOLD
ADR
DAS
CS
Figure 4. Bus Slave Write Timing
P R E L I M I N A R Y
Am79C90
The bus transceiver controls, DALI and DALO, are used
to control the bus transceivers. DALI directs data toward
the C-LANCE, and DALO directs data or addresses
away from the C-LANCE. During a read cycle, DALO
goes inactive before DALI becomes active to avoid
“spiking” of the bus transceivers.
Write Sequence (Master Mode)
The write cycle is similar to the read cycle except that the
DAL00 – DAL15 lines change from containing ad-
dresses to data after either ALE or AS goes inactive.
After data is valid on the bus, DAS goes active. Data to
memory is held valid after DAS goes inactive. Refer to
Figure 5-2.
Write Data
O.D.
17881B-10
AMD
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