Vector 4 - Page 106

EXHIBIT
1l-21
XON/XOFF
SERIAL
PROTOCOL
This
serial
printer
protocol
uses
the
XON/XOFF
type
of
"Software
Handshaking".
The
printer
sends
a
XON
byte
when
it
is
ready
to
receive
data
and
.a
XOFF
byte
when its buffer is full
3':. .. f'..:'. j— .n. -'.'..':'.' . ¢ S
USART
o
dotal
et
e
oo
BUFFER
ese’lsoy s
. .’ oo
Ll
PRINTER
------ Software/Hardware may
M 1 CONTROL SEQUENCE send initialization
ssamT Qo i rl’}“f”} B sequence. Depends on
— | Lk printer protocol.
SATER
PRINTER
i i [ Printer sends XON signal
. to USART indicating it is
USART , XON ‘ B BIUT Efi T] ready to receive data.
i i - PIN 2
PAPER
PRINTER
"_l' USART sends data to
f 1 DaTA !i printer. Buffer fills and
printer starts printing.
PIN 3
I
PRINTER PAPE
_ _ K Printer buffer is full.
BUFFER M' Printer sends XOFF signal
-
—
}111
continues
printing.
T L
PAPER
PRINTER
T Printer buffer is
ppmeseeege
§
1
]
é
[
1
TU}FE
ij{
1
i”:ii
;mé)b%]lng_.
;’ln
e;
se?
S
| < ON i ] signal. rinter
i | %I;igi continues printing
PIN 2 !;!
L il
PAPER
PRINTER
USART sends data to
T 1 BUFFER printer. Printer continues
o b printing.
II 5-15