Question 11.23: Discuss the program ROM space allocation for each of the fol...
Discuss the program ROM space allocation for each of the following cases.
(a) EA = 0 for the 8751 (89C51) chip.
(b) EA = V_{cc} with both on-chip and off-chip ROM for the 8751.
(c) EA = V_{cc} with both on-chip and off-chip ROM for the 8752.
(a) When EA = 0, the EA pin is strapped to GND, and all program fetches are directed to external memory regardless of whether or not the 8751 has some on-chip ROM for program code. This external ROM can be as high as 64K bytes with address space of 0000 – FFFFH. In this case an 8751(89C51) is the same as the 8031 system.
(b) With the 8751 (89C51) system where EA = V_{cc}, it fetches the program code of address 0000 – 0FFFH from on-chip ROM since it has 4K bytes of on-chip program ROM and any fetches from addresses 1000H – FFFFH are directed to external ROM.
(c) With the 8752 (89C52) system where EA = V_{cc}, it fetches the program code of addresses 0000 – 1FFFH from on-chip ROM since it has 8K bytes of on-chip program ROM and any fetches from addresses 2000H – FFFFH are directed to external ROM