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21
RAM Socket pin layout
1
2
3
4
5
6
7
8
9
10
11
12
13
14
A14
A12
A7
A6
A5
A4
A3
A2
A1
A0
I/O0
I/O1
I/O2
Vss
Vcc
WE
A13
A8
A9
A11
OE
A10
CS
I/O7
I/O6
I/O5
I/O4
I/O3
28
27
26
21
25
24
23
22
20
19
18
17
16
15
Address Latch
.
The board connections are for a 74HC573 device. This device will operate reliably with the 4 MHz
crystal supplied but if a faster crystal is inserted, a faster version of this device may be required -
74AHC573 or 74FHC573. Note that this option will alter the EMC characteristics of the board and
the CE mark will no longer be valid without re-testing.
Using Expansion Header
The expansion header (marked Memory Expansion) can be used for memory mapped
peripherals. The Chip Select (CS) line is connected which gives compatibility with most popular
microcontroller peripheral devices e.g. memory, PIAs, timers etc.. The header is mapped from
$0000 to $FFFF, but internal memory will take precedence.
The address latch chip (74HC573) must be inserted before the expansion header can be used,
but the RAM chip can be omitted.
