ZiLOG Z8 Technical Manual

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PROGRAM
Z8881
MEMORY
P01
2a
Ag
(4K BYTES)
112 PORT 0 <
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2b
P02
LS157
A10
3a
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3b
P03
4a
A11
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The initialization routine is mapped in the first 256 bytes of program memory. Any memory write
operation
will cause the flip-flop to select Port 0 outputs as addresses.
Figure 7-4. Example Z8681/Hemory Interface
Port 0 is programmed for memory operation by writ-
ing the appropriate bits in the Port 0-1 Mode reg-
ister (Figure 7-5). The proper port initializa-
tion sequence is:
• Load Port 0 with initial address value.
• Configure Port 0-1 Mode register.
• Fetch the next three bytes without changing the
address in Port O. (This is necessary due to
instruction pipelining.)
R248 P01M
Port 0-1 Mode Register
(% F8; Write Only)
P0
4
-P0
1
MODEI
OUTPUT = 00
-r- PO
a
-P0
3
MODE
L 00 = OUTPUT
01 = INPUT
1X = As-All
INPUT = 01
A
12
-A
15
= 1X
Figure 7-5. Z8681 Port 0 Memory Operation
The lower nibble of Port 0 can be defined as
address lines A
8
-A11' by setting D1 to 1.
Similarly, setting D7 to 1 defines the upper nib-
ble of Port 0 as address lines A12-A15.
Whenever
Port 0 is configured to output address
lines A
12
-A
15
, A8-A11 must also be selected as
address lines.
7.3.2 Z8682 Initialization
The Z8682 must be operated in Test mode only.
Section 8.4 gives a complete description of the
proper technique for entering Test mode.
The
user initialization routine must begin at
location %812 and must reside in memory fast
enough for normal memory timing. In the Z8682,
the user is not protected from reconfiguring
Port 1 by writing to R248 (P01M). Therefore
whenever a write is made to P01M, the value 10
(binary) must be written to bits D4 and D3. Any
other value will cause complete loss of program
control.
3047-060,3047-007 7-3

ZiLOG Z8 Specifications

General

Brand	ZiLOG
Model	Z8
Category	Desktop
Language	English