Reflex Lexicon - Z80 Processor and Memory Map Details

Theory
of
Operation
Lexicon
Z80,
ROM,
RAM,
A Z80
microprocessor
(U1
2)
is
utilized
as
the Host Processor
for
the
Reflex.
Memory Map
its
primary
responsibilities
are:
•
Processing
of
data and
instructions
to
and
from
the UART
(U2)
•
Processing
of
data
and instructions
to
and
from
the
Lexichip
II
(U14)
•
Handling
of user control
and
front
panel display
48Kbytes of
ROM
space
are
used
in
a
single
27C512
PROM
(U8).Audio
effects,
diagnostics,
I/O and
housekeeping
subroutines
are contained
in
this
memory
space.
The Z80
scratch
pad
memory
is 8Kbytes
SRAM. This RAM
(U9) space
is
volatile
and any
system parameter changes made must
be
copied into
EEPROM
(U7)
to be
saved on power down.
The Lexichip II
contains
its
own
on-board
program RAM
and
I/O
registers
which are
addressable
by
the
Z80. The Lexichip
II
occupies
IK
of the Z80’s
64K
addressable memory
space.
The
address
decoding
scheme is
very simple. Memory mapping
is
used
exclusively.
The memory
map consists of:
one
48k
block
for
ROM, one 8k
block
forSRAM,
and
eight
1 k
blocks
for
I/O and
peripherals,
of
which onlyfour
1
K
blocks are
used.
The
decoding circuitry consists of three sections:
(U1
1
)
HC14
inverter,
one
section of
{U42)
OR
gate
and
(U10)
HC138,
a 3 to 8
demultiplexer.
SIZE
SIGNAL
DESCRIPTION
EOOO
-
FFFF
8k
RAM/
RAM
select
DCOO
-
DFFF
1k N/C
Not used
D800
-
DBFF
1k
N/C
Not
used
D400
-
D7FF
Ik
N/C
Not used
DOOO
-
D3FF Ik
N/C
Not used
CCOO
-
CFFF
Ik
102/
Output Register
2
select, ORed with
WR/
Input
Register
2
select, decoded at chip
by
RD/
C800
-
CBOO Ik
I01/
Output
Registerl select, ORed with WR/
Input
Register 1 select, decoded at chip by RD/
C400
-
C7FF Ik
UART/ UART
select
COOO
-
C3FF Ik
LEX/
Lexichip
select
0000
-
BFFF 48k
EPROM/
ROM select
64k Total Z80 memory
space
4-4