CHAPTER 3 INTERFACE
B-EP Series
3-3
3.2.2 INPUT/OUTPUT SIGNAL
• RD (Host → Printer)
A data signal which the printer receives from the host.
Logic 1 is Low level, while logic 0 is High level.
It is in a Low state when no transmission is in progress.
• SD (Printer → Host)
A data signal which the printer sends to the host.
Logic 1 is Low level, while logic 0 is High level.
It is in a Low state when no transmission is in progress.
3.2.3 TRANSMISSION CONTROL
The host performs transmission control with a NAK (15H)/ACK (06H), which means the printer is
ready, a link request PAD (FFH), and a command packet.
c Link request (Host → Printer)
The host should send a link request PAD (FFH) in order to link to the printer. The link
request PAD should be intermittently sent until the printer is linked and enters a ready state.
d Printer ready (Printer → Host)
When the printer detects the link request PAD from the host and enters a ready state for
receiving the command packet, the printer sends a NAK within 40 msec. When an error such
as CRC occurs, the printer sends a NAK.
NAK
15H
The printer sends an ACK, when the printer properly receives the command packet and enters
a ready state for receiving the next data, or when the data is stored into flash ROM.
ACK
06H
e End of link (Host → Printer)
When there is no packet to be sent, the host sends an EOT to end the link.
EOT
04H
f Turnaround time
The printer should send a NAK/ACK/status packet after 5 msec. from when a PAD/command
packet has been received.
g Time out
Host: Time out due to waiting for a NAK after a PAD is sent ................................ 50 msec.
Time out due to waiting for an ACK after a command is sent ..................... 200 msec.
Printer: Time out due to waiting for a command after a NAK is sent ....................... 1 sec.
Time out due to waiting for an EOT or a command after an ACK is sent ... 1 sec.
Time out due to waiting for an EOT after the status is sent ........................ 1 sec.
h Status packet (Printer → Host)
If the printer enters an error state when the command is sent from the host, or when status
transmission is requested, the printer sends a status.
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