Jameco Electronics 3000 用户手册

Parallel Port E, shown in Figure 9-2, has eight I/O pins that can be individually pro-
grammed as inputs or outputs. PE7 is used as the slave port chip select when the slave port 
is enabled. Each of the port E outputs can be configured as an I/O strobe. In addition, four 
of the port E lines can be used as interrupt request inputs. The output registers are cas-
caded and timer-controlled, making it possible to generate precise timing pulses.