Sonic Alert msm80154s, msm83c154s, msm85c154hvs Outline, Port 0 internal equivalent circuit

MSM80C154S/83C154S/85C154HVS

5. INPUT/OUTPUT PORTS

5.1 Outline

MSM80C154S/MSM83C154S is equipped with four 8-bit input/output ports. The functions of these four ports (port 0, 1, 2, and 3) are listed below.

1)Port 0: Input/output bus port, address output port, and data input/output port.

2)Port 1: Quasi-bidirectional input/output port and control input pin.

3)Port 2: Quasi-bidirectional input/output port and address output port.

4)Port 3: Quasi-bidirectional input/output port and control input/output pin.

5.2Port 0

Port 0 is an 8-bit input/output port. The circuit configuration is shown in Figure 5-1. When port

0 is used as an input/output port in internal ROM mode (MSM83C154S), the equivalent circuit is indicated in Figure 5-2. When operated as an output port, port 0 becomes an open drain output port, and when operated as an input port, “1” should be set in the port 0 latch to put the port 0 pin into floating status prior to using the port for input purposes.

When port 0 is used in external ROM mode (MSM80C154S) and external RAM mode, the equivalent circuit is shown in Figure 5-3 where addresses and data outputs are obtained as “1” and “0” by totem pole output driver. When data from external ROM or external RAM is applied as input data, port 0 automatically becomes a tri-state input port. When the CPU is reset or when an external ROM or external RAM is accessed, “1” data is set automatically in the port 0 latch. The port 0 pin table is shown in Table 5-1.

PD/DATA
PC0~7
RA0~7	INTERNAL
ACC0~7
	BUS	VCC
	D	Q
		P
	WPO	PORT 0
		N
MODIFY
READ
FLOATING
	Figure 5-1	Port 0 internal equivalent circuit

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