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4.3.3
Initial Operation (See Time Chart (1), Fig. 4-8.)
When the Power switch is turned ON, C3, which is connected to
Q2, generates a RESET signal, which clears the processor.
After RESET goes HI (40 - 80
~s),
the program starts and
returns the carriage to the home position.
If the carriage is
already home, it is moved out of the home position then returns.
During initial operation, BUSY (at CN6-11) is HI ("1") and data
is not accepted.
When initialization is complete, BUSY goes
LO to make the printer ready.
To prevent eroneous operation during power ON/OFF, transistor
TR2 delays the bias current to the drive circuits, and turns it
off in advance.
4.3.4
Data Input (See Time Chart (1), Fig. 4-8.)
8-bit parallel data is input to PAO-PA7 of Ql.
Data is latched
into Ql on the rising edge of STROBE, an interface signal provided
by the host controller at CN6-1 and connected to Ql-39 (PC2).
When the input buffer of Ql is full (one character received) it
raises Ql-37 (PCD) which is the interrupt line to Q2.
This HI
develops a LO at Q5-8, which causes BUSY to go HI at Q7-8.
INT at Q2-6 caused the
~CPU
to read the character received, which
is on the
~CPU
data lines DBO-DB7.
The
~CPU
decodes the character.
If this is a data character, it
is returned to Ql's RAM and stored in the line buffer.
If the
character is a CR or LF, a print operation or feed operation is
initiated.
After the character is processed, the· ACKNOWLEDGE
pulse is sent to the interface via Ql-l (PC3).
Also, BUSY is
dropped to allow the next character to be strobed in.
This
process is repeated until the Line Buffer is full or CR LF is
received.
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