com90c66 Standard Microsystems Corp., com90c66 Datasheet - Page 42

• Manufacturer Part Number: com90c66
• Description: Arcnet Controller/transceiver With At Interface And On-chip Ram Corporation
• Manufacturer: Standard Microsystems Corp.

address to be accessed through the Data
Register. If a 1K x 16 space is desired, the A0
bit should be forced to a logic "0" and A1-A10
will be used to load the Address Pointer
Register. A single byte access at the defined
word address is still possible by accessing
either the upper or lower portion of the Data
Register.
Auto Increment Mode, the access to the upper
portion of the Data Register automatically
increments the pointer.
Vs. I/O Cycles section of this document for
further information on Sequential I/O Mapped
* Any combinations other than those defined above are illegal.
**This access will increment the pointer
8-Bit I/O
Accesses
8-Bit Memory
16-Bit I/O
Accesses
16-Bit Memory
Accesses
When the device is configured for
Address Pointer Low
Register
Address Pointer High
Register
Data Register
Other Registers
RAM Access
Pointer Register
Word
Address Pointer Low
Register
Address Pointer High
Register
Data Register Word
Even RAM Byte
Odd RAM Byte
Other Registers
RAM Access, Word
Even RAM Byte
Odd RAM Byte
ACCESS
Table 14 - 8-Bit vs. 16-Bit Signal Level Requirements*
Refer to the Memory
A0
X
X
X
X
0
1
0
0
1
0
0
1
0
0
1
nSBHE
42
X
X
X
X
X
0
1
0
0
1
0
X
0
1
0
Memory cycles and the Auto Increment Mode.
Refer to Table 14 for signal level requirements
in 16-Bit I/O Mapped Mode.
16-Bit Memory Mapped Mode:
In 16-Bit Memory Mapped Mode, the A10-A1
lines of the Address Bus determine the word
address to be accessed, while A0 and nSBHE
determine which byte within the word location
will be accessed. Refer to Table 14 for signal
level requirements in 16-Bit Memory Mapped
accesses.
nIOCS16
X
X
X
X
1
1
1
1
0
0
0
0
0
0
1
nMEMCS16
X
X
X
X
X
X
X
X
X
X
X
1
0
0
0
TRANSFER
D8-D15**
D8-D15**
D0-D7**
D8-D15
D8-D15
D8-D15
D8-D15
D0-D7,
D0-D7,
D0-D7,
D0-D7
D0-D7
D0-D7
D0-D7
D0-D7
D0-D7
D0-D7
D0-D7
DATA