Ian May
2013-11-03 13:19:48 UTC
The "My understanding of the N8VEM 6x0x boards" v2(1).doc document on the
wiki under the "Obtaining the parts" section on the mezzanine board on page
10 states "The 6522 is also available new from Mouser etc. Buy the S
(Standard CMOS) version".
One of the key differences between the W65C22S and W65C22N is the circuitry
connected to the IRQ pin. The W65C22N has an open drain output like all the
previous NMOS and CMOS parts and it can be wire ORed with the IRQ pins of
other devices. The W65C22S has a standard totem pole output, so in a wire
ORed system if another device attempts to pull the IRQ line low there will
be a short across the 5V supply between the pull-up transistor in the W65C22S
and the device pulling the line low. If you wish to use the W65C22S in a
wire Ored system the data sheet suggests using "a low voltage diode (<0.5V)
in series with the W65C22S totem pole IRQB output." See page 31 of the
W65C22 data sheet.
The correct device to use with the mezzanine board is the W65C22N.
Cheers,
Ian.
wiki under the "Obtaining the parts" section on the mezzanine board on page
10 states "The 6522 is also available new from Mouser etc. Buy the S
(Standard CMOS) version".
One of the key differences between the W65C22S and W65C22N is the circuitry
connected to the IRQ pin. The W65C22N has an open drain output like all the
previous NMOS and CMOS parts and it can be wire ORed with the IRQ pins of
other devices. The W65C22S has a standard totem pole output, so in a wire
ORed system if another device attempts to pull the IRQ line low there will
be a short across the 5V supply between the pull-up transistor in the W65C22S
and the device pulling the line low. If you wish to use the W65C22S in a
wire Ored system the data sheet suggests using "a low voltage diode (<0.5V)
in series with the W65C22S totem pole IRQB output." See page 31 of the
W65C22 data sheet.
The correct device to use with the mezzanine board is the W65C22N.
Cheers,
Ian.
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