Epson LQ-1500 Service Manual page 65

1. The return side, i.e. a twisted pair return, is connected to the signal ground ground level. A twisted pair
line must also be used for each signal for the interface and to connect the return side. To effectively pre-
vent noise, shield this signal line cable and connect it to the enclosure grounds of the host computer and
printer, separately.
2. All interface condition are TTL based. The rise and fall times of each signal shall be less than 0.2 @sec.
3. For details of the timing of each signal, refer to the timing chart.
4. Fata should be transferred to the printer after checking pulse ACKNLG or when signal BUSY
5. Signal AUTO FEED XT can be fixed to LOW when DIP switch SW2-3
6. When ACKNLG and STROBE are connected with the interface connector, DATA1 to 8 are set to an ap-
propriate character code ("1 " at open against GND, "0" at short). A printing test including that for the in-
terface circuit can be executed without external equipment.
3.1.3 Operating principle
3.1.3.1 Data entry
As the interface board (IUPIF) is non-buffered, a 2 K-byte RAM on the main board (UXMCL) can serve as an
input (reception) buffer. This option is selectable via DIP switch setting on the interface board.
3.1.3.2 Buffer full/empty control
Since signal BUSY is LOW until the 2 K-byte input buffer becomes full, the data from the host com-
puter is entered in the input buffer on the UXMCL board through 8255AC-5.
At the same time, developing the print pattern for one line starts for the 7 K-byte print buffer by Z-80A
CPU on board UXMCL. When the input buffer is partly empty, the data is entered, even during printing
or line feed. When the input buffer is full, the BUSY signal is HIGH, data entry is prohibited.
(2) When the input buffer
The data is entered in through Interface 8255AC5 byte by byte. When 2 bytes of data are entered,
signal BUSY becomes HIGH to prohibit data entry.
At the same time that the data is entered in the buffer, a print pattern is developed for the print buffer
by Z-80A CPU on board UXMCL.
Table 3.5
invalid
IS
set ON.
IS
3-4
LOW.
IS