I/O Control; The Fga - HP PageWriter XL M1705B Service Manual

I/O Control
The I/O control circuitry handles the system input and output. The
block diagram in Figure 5-G shows the major elements.
The FGA
The primary element in the I/O control is the "Foundation" gate
array (FGA). It provides the following functions:
H Keyboard interface
n
Data bus arbitration
w Transmit portion of the patient module interface
n
Enable and Select generation
w System clock generation
n
Baud rate generation
The FGA, in its role as keyboard interface, sends and receives
data directly to and from the keyboard through a 1200 baud serial
interface.
As data bus arbitrator, the EGA enables and controls the direction
of the data transceivers that buffer system data. The FGA also
generates the read and write enable signals and the chip select signals
for all I/O devices.
5-12 Theory of Operation