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Using Internal Reference
To use the internal (on-board) Voltage Reference, the pot marked
AREF
is used to set the voltage
level. The voltage level can be measured with a meter connected to the header pins labeled
Analog Ref and Analog Gnd in the above diagram or from the two holes marked Meter (+ and -).
Using External Reference
To use the A2D 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
diagram above.
Dual Rail Power Supply
An dual rail power supply is included - marked OP-AMP. It is design to provide a low current
(<2mA) supply for external operational amplifiers for signal conditioning etc. on the ADC inputs. It
is designed to 10V and -10V, but this may vary especially if the RS232 is being used.
Using Real Time Clock
A 32768 Hz crystal is connected to TOSC1 and TOSC2 pins - Pin 19 and Pin 18. This can be
used to generate a 1 second pulse by setting Timer 0 to Asynchronous Operation - see data book
for details.
Using External RAM
The AT90MEG103 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).
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.
The RAM is memory mapped to $8000..$FFFF.
