Intel 8XC251SQ, 8XC251SA, 8XC251SP manual Example 4 RD10 = 10, 16-bit Bus, External RAM, Prom/Eprom

8XC251SA, SB, SP, SQ USER’S MANUAL

13.8.4 Example 4: RD1:0 = 10, 16-bit Bus, External RAM

In this example, an 87C251SB/83C251SB operates in nonpage mode with a 16-bit external ad- dress bus interfaced to 64 Kbytes of RAM (Figure 13-23). This configuration leaves P3.7/RD#/A16 available for general I/O (RD1:0 = 10). A maximum of 64 Kbytes of external memory can be used and all regions of internal memory map into the single 64-Kbyte region in external memory (see Figure 4-6 on page 4-11). User code is stored in on-chip ROM/OT-

PROM/EPROM.

83C251SB	VCC	RAM
		(64 Kbytes)
87C251SB
EA#		CE#
P2		A15:8
P0	Latch	A7:0
		D7:0

WR# PSEN# OE# WE#

A4221-01

Figure 13-23. Bus Diagram for Example 4: 87C251SB/83C251SB in Nonpage Mode

13-24