Information Technology Reference
In-Depth Information
Data register
2
D0
9
D7
Control register
1
STROBE
14
AUTOFEED
16
INIT
17
SELECT INPUT
Figure 16.4
Output lines
16.4.3 Inputs
There are five inputs from the parallel port (BUSY,
ACK
, PE, SELECT and
ERROR
). The
status of these lines can be found by simply reading the upper 5 bits of the status register, as
illustrated in Figure 16.5.
Status register
15
ERROR
13
SELECT
12
PE
10
ACK
11
BUSY
Figure 16.5
Input lines
Unfortunately, the BUSY line has an inverted status. Thus when a LOW is present on
BUSY, the bit will actually be read as a 1. For example Program 16.3 reads the bits from the
