Advertisement
j.~3;~~?O
P
l' () C ~~
s
~:;
()
f'
r1
0
cI u
1
e
L3220-91
OB'7
/10
Rev
JAN-'O 4···82
The keyboard/display port also enables a counter
(U114)
which
counts
horizontal sync pulses down to a bell frequency.
The
bell
signal is
the n
~:;
hap
(~d
b Y
(~4
a n
cI
i
t~:;
a ,;) soc i ate d c: i
l'
cui t .
T
I'\(~
reM a i n i n g bit
S
0
f
the
I«~~
y
boa
l'
d / d i
~;
P
:I.
e)
y
POl" t d
E-~
t
(;H'
Min
E~
w h e t h
£o~
r
£om han c
£o~
Men t
<.!;
will
b e
enabled
and latches
the
signal
which
deterMines
the blinkrate
of
blinking characters.
The
NNMI
(non-Maskable
interrupt)
signal
to
the
ZaOA
is
Masked
externally by a D flip-flop
(half of U612).
Port addresses B8H to 8FH
select the NENNMI signal of the port decoder,
clocking the latch while
address bit TAO is the data input.
This Means that a write to port 88H
clears the latch,
disabling NMI,
while a
write to
port 89H sets the
latch f.·H\i:\bling NMI.
The systeM status port,
U36, located at address 90H allows the ZaOA to
l' (.:~
a d t h
E~
V (~H'
tic alb 1
elf)
k s i 9 n a 1
( VB
l.
A N K) f
0 f'
S
Y n
c:
h
l' 0
n i z i n g the s of twa
l'
e
with the hardware.
It also provides the inputs
f~r
the datacoMM status
signals discussed above and also Monitors the integral printer
s~atus.
The integral printer
port at address
98H buffers data continuously to
the
printer
bus,
the data being
latched
in
the
printer when
the
NPRINTER signal is active.
The processor writes data and
COMMands to
the printer
via U16 and half of U1S.
Printer control is specified by
perforMing a write operation to the
printer with address lines TAO and
TA1 and data lines TDO-TD7 selecting the particular function.
Printer
status is read back frOM the printer on the upper
half of U1S which is
enabled for read operations frOM the printer port.
The presence of the
printer is
detected by
reading
status
frOM the printer and checking
data bit TU1.
TU1 will be
low if the printer is not connected due to
the pullup resistor R1.
When the printer is connected to the processor
Ji pin 11 is pulled low by the printer therby indicating connection.
Each
character in the printer is forMed by 30 bytes of dot data,
each
pair
of
bytes
being Made
up of
the dot
data
needed
to forM
the
character if
the
character
cell is scanned horizontally.
The first
byte in
the pair
indicates the state of
every other dot
while seven
bits
of the following byte indicate the state of the interstitial dots
for the saMe horizontal scan.
Thus fifteen pairs
of.bytes correspond
to
fifteen
horizontal
scans
of
the character.
In
this
way
any
character font in a 1S by 1S cell May be created.
The printer buffers
the data
and
translates the horizontal dot
inforMation into vertical
dots for
printing.
Each 30 bytes of dot data are followed by a print
COMMand to print the character.
The printer is also able to print
in
expanded and cOMpressed Modes.
The
reMaining
TBUS
port
located
at ASH latches SOMe signals to the
video section and one for the datacoMM
section.
The NMODEM signal is
inverted to provide the clock for the latch (U3S).
Advertisement
