Electronics America Computer Hardware User Manual

PD78214 Sub-Series

5.5.1 Hardware Configuration

Fig. 5-21 shows the hardware configuration of port 4.

Fig. 5-21 Block Diagram of Port 4

5.5.2 Setting the I/O Mode and Control Mode

The memory expansion mode register (MM, see Fig 13-1) specifies the operating mode of port 4, as listed in Table

5-5.

Table 5-5 Port 4 Operating Modes

MM2

MM1

MM0

EA pin

MM register bit

Operation mode

Input port

Output port

Address/data bus

(AD0-AD7)

For the

PD78213, port 4 functions only as the address/data bus (AD0 through AD7).

Internal data bus

WRPUO

Pull-up resistor option register

PUO4

WRP4n

RDP4n

RDPUO

Output latch

P4n

n = 0 to 7

VDD

MM0-MM2 EA

Internal address bus

I/O control circuit

P4n