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Communication Interfaces 10-5
The following figure shows a simplified block diagram of the printer
receive buffer and the data path between the host and the print
mechanism.
The host transfers characters in the form of 7-bit or 8-bit data bytes,
depending on which character set is selected. To ensure that no data
is lost between the host and the printer, all data-transfer operations
involve the following steps.
1. The host transfers characters via the communication interface
into the printer receive buffer and then the printer transfers them
at a fixed rate from the receive buffer to the print mechanism.
2. If the host-to-receive buffer transfer rate exceeds the buffer-to-print
mechanism transfer rate, the receive buffer eventually approaches
its capacity.
3. The printer signals the host to suspend data transfer operations
as the printer continues to transfer characters at a fixed rate from
the receive buffer to the print mechanism.
4. When the supply of characters in the receive buffer is sufficiently
depleted, the printer signals the host that it is ready to receive
additional data.
host
communication
interface
printer receive buffer and associated data path
printer
receive
buffer
print
mech.