Atmel megaAVR, Getting Started

Page: 21 / 28

Board Applications
megaAVR™ Starter Kit Manual 9-3
header pins labeled “Analog Ref” and “Analog Gnd” in the previous diagram or from the
two holes marked Meter + and -.
9.3.3 Using External
Reference To use the A/D converters with an external Voltage Reference, the link marked “LK1”
must be cut. The voltage is applied to the pins marked “Analog Ref” and “Analog Gnd”
on the Analog header—see previous diagram.
9.4 Using External
RAM
The ATmega103 can be used with external SRAM. A socket is provided for a 28-pin
RAM chip and for an address latch chip. These are next to the device adapter at the top
of the board. There is also a header for further memory expansion, which is connected
through the address latch. The pin functions are marked on the board, including chip
select (CS).
9.4.1 RAM
Recommendations A low power 62256 SRAM is suggested with an access time of 70 nS. If a very fast RAM
is required, the crystal frequency may need to be increased. If a much slower SRAM is
used, the SRAM Wait State bit must be enabled in user software–—see data book. The
layout of the 28-pin RAM socket is shown below, and any RAM with this pin-out could
be used.
9.4.2 RAM Socket Pin
Layout
9.4.3 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
E MC c ha ra ct e rist i c s o f t he bo a rd a nd th e C E m a rk wi l l n o l o ng e r b e v a l i d
without retesting.
9.5 Using LCD
Connections
The header marked LCD interface is for a standard 2 x 16 LCD. The connections are
shown on the board and in the following table.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
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
Connection Name Function
0V Ground
+5 V
CC
- must be 5V
Vo Contrast
RS Register Select- A14
Wr Not Write
E Enable
D0 Data Bit 0