ZiLOG Z80 series, User Manual

Page: 13 / 34

12
SW1
Image Qty Reference Description
1
SW1 DIP switch, 6 way, piano style
Supplier Part number
eBay 262361463572
Farnell 2452331
Mouser 653-A6FR-6104 (black)
RS 877-2359
This switch is used to set the I/O address for the module. It sets the required state of
address lines A2 to A7, thus allowing the module to occupy a 4 address block on any
4-byte boundary.
In order to provide some certainty for software it is strongly recommended you set
the base address of your first PIO module to 0x68, so that the module occupies I/O
addresses 0x68 to 0x6B. This is done by setting switches 1 to 6, to On, Off, Off, On,
Off, On where On is the switch closed. In the case of the piano style DIP switch, the
On position is the switch lever pushed down towards the circuit board.
Switches in the On position pull down the input of the address comparator U1.
Switches in the Off position allow the input of the address comparator to be pulled
up by RP1.
U1
Image Qty Reference Description
1
U1 74HCT688, 8-bit identity comparator, PDIP 20
Supplier Part number
Farnell 2407104
Mouser 595-CD74HCT688E
RS 663-0650
This integrated circuit provides the address decoding, by comparing the current
address from the CPU with the address set with the DIP switch SW1.