ÉlanSC310 Microcontroller Evaluation Board User’s Manual
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Programmable General Purpose (PGP) Pins
The ÉlanSC310 microcontroller has four Programmable General Purpose (PGP)
pins which can be set up as inputs, outputs, address decodes, and address decodes
that are gated with the I/O read or I/O write pulse. Index registers for the PGP pins
are write only. Keep this in mind when writing to Index 91h, which controls all
PGP pins.
Remember, this particular implementation of the PGP pins is specific to the
ÉlanSC310 microcontroller evaluation board only. Other system designs may
implement these pins differently.
The ÉlanSC310 microcontroller evaluation board makes use of the PGP pins as
follows.
PGP0
This pin in used to clock data from the data bus into a flip-flop that is used to control
the programming voltage to the ROM sockets. PGP0 must be set up to gate with
the I/O Write Command. This is done by setting the ÉlanSC310 Index 91h to
xxxxxx10b. Index 89h is used to set up the I/O address for PGP0. Setting Index
89h to a 20h programs PGP0 to respond to writes to I/O addresses 100h–107h.
PGP0 must also be enabled as an output. This is done by writing bit 6 of the
ÉlanSC310 Index 70h to a 1. By programming this pin as just described, the
ÉlanSC310 microcontroller is now able to write to the 1 bit register at I/O port
100h. When set up as described, the write-only register at I/O address 100 is as
shown in the table below.
NOTE:
This pin is referenced as PGPA on the evaluation board schematics
beginning in “Schematics” on page D-1.
Table 4-1. I/O Address 100–107
Bit
Description
7–3
Reserved
2
1 = V
PP
line to ROM sockets set to 12 V
0 = V
PP
line to ROM sockets set to 5 V
1
Not used
0
Not used
evalbd.book : ch4 Page 2 Thursday, August 8, 1996 2:34 PM