com90c66 Standard Microsystems Corp., com90c66 Datasheet - Page 64

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

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These corrections apply to this data sheet only when used for Revision D of the COM90C66. This
COM90C66 revision is identified on the part by either the letter "D" preceding the date code or no letter
at all preceding the date code.
Specific entries in table format appear on the following pages.
The Revision D device contains 16-bit detection circuitry on the input of pin 60 to allow the device
to power up in 16-bit mode.
writing to the Configuration Register, the device defaults to 16-bit mode. If a low level is not
sensed on pin 60, the device defaults to 8-bit mode. The mode may be overridden via software, if
desired.
In the generation of the nMEMCS16 signal, the Revision D device decodes the A19-A11 addresses
before they are latched by the device. The earlier comparison allows the nMEMCS16 signal to be
activated and deactivated more quickly by being independent of the BALE signal.
In the generation of the nIOCS16 signal, the Revision D device decodes the A15-A2 addresses
before they are latched by the device. The earlier comparison allows the nIOCS16 signal to be
activated and deactivated more quickly by being independent of the BALE signal.
In the Revision D device, when the IOCHRDY signal is negated for internal accesses, it is always
negated for two to three XTAL1 clock periods rather than one to two.
In the Revision D device, the leading edges of the nMEMR and nMEMW signals internally latch
the addresses. When the device is used in 8-bit mode, the BALE signal should be tied high. In
this case, the 16-bit cycles which get broken into two 8-bit cycles will now be addressed properly
for both cycles because the ALE signal is no longer depended upon.
requirement of the ALE signal should be disregarded.
DATA SHEET ERRATA FOR REVISION D COM90C66
If pin 60 senses a low level any time between hardware reset and
ADDENDUM 2
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Any reference to the