DIY Southern Cross II Hardware Handleiding - Pagina 6

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As mentioned previously, these are "dynamic" not static ports. With referrence to sheet 2 of the schematic
diagram, the 8 I/O lines are actually driven by the data bus (BAD0 - 7). The ports are formed by decoding a
256 byte memory block and using the resulting output as an active low strobe, similar to the chip enable
signals for the EPROM and RAM chips. These 4 bit ports are mapped in external data memory at the
following address locations:
Bit port 1
Bit port 2
Bit port 3
Bit port 4
Although each port is mapped into a 256 byte block, it is only one address "wide". Therefore bit port 1 can
be accessed at address FC00h, FC01h, FC02h ... etc right through to FCFFh. These ports are both input and
output ports, depending on the instruction used to access them.
These ports are pin for pin compatible to the CN1 port on the Z80 based "Southern Cross" computer, also
available from DIY Electronics. It is provided on the Southern Cross II to take advantage of a number of add-
on boards already available for the "Southern Cross" computer.
The bit ports are brought out to a 16-pin header labelled J4.
J4 pin
1
3
5
7
9
11
13
15
A maximum of 256 bytes of I/O expansion is available via connector J3. This interface allows for further
devices to be connected to the microcontroller. The interface is mapped in external data memory beginning at
address location F800h.
J3 pin
1
3
5
7
9
11
13
15
17
19
21
23
25
Signals preceeded by " / " are active low, all other signals are active high.
Bit Ports - J4
FC00h
FD00h
FE00h
FF00h
Signal
J4 pin
+5V
2
/BIT PORT 1
4
/BIT PORT 3
6
GND
8
BAD4
10
BAD5
12
BAD6
14
BAD7
16
I/O Expansion Interface - J3
Signal
J3 pin
A0
2
A2
4
A4
6
A6
8
AD0
10
AD2
12
AD4
14
AD6
16
/RD
18
RESET
20
/IOEXP
22
+5V
24
GND
26
Signal
/RESET
/BIT PORT 2
/BIT PORT 4
GND
BAD3
BAD2
BAD1
BAD0
Signal
A1
A3
A5
A7
AD1
AD3
AD5
AD7
/WR
ALE
+5V
GND