Intel mcs-48 manual Test and Debug, Single Step, Disabling Internal Program Memory, Reset

SINGLE COMPONENT SYSTEM

The ProgramlVerify sequence is:

1.Voo = 5v, Clock applied or internal oscillator operating, Reset =Ov Test 0 = 5v, EA = 5v, BUS and PROG floating

2.Insert 8748 in programming socket

3.Test 0 = Ov (Select Program Mode)

4.EA = 23V (Activate Program Mode)

5.Address applied to BUS and P20-1

6.Reset = 5v (Latch Address)

7.Data applied to BUS

8.Voo = 25v (Programming Power)

9.PROG = Ov followed by one 50ms pulse to 23V

10.Voo = 5v

11.TEST 0 = 5v (Verify Mode)

12.Read and Verify Data on BUS

13.TEST 0 = Ov

14.Reset = Ov and repeat from Step 5

15.Programmer should be at conditions of Step 1 when 8748 is removed from socket.

2.4Test and Debug

Several MCS-48 features described in the previous sections are discussed here to emphasize their use in testing MCS-48 components and in debugging MCS-48 based systems.

2.4.1 Single Step

Single step circuitry within the micro- computer in combination with the external circuitry described in Section 2.1.13 allows the user to execute one instruction at a time whether the instruction is one or two cycles in length. After completion of the instruction the processor halts with the address of the next instruction to be fetched available on the eight lines of BUS and the lower 4-bits of port

2.

P23

P22

P2l

P20

DB7

DB6

DB5

DB4

DB3

DB2

DBl

DBO

ADDRESS OUTPUT DURING SINGLE STEP

This allows the user to step through his program and note the sequence of instruc- tions being executed.

While the processor is stopped, the I/O information on BUS and the 4-bits of port 2 is, of course, not available. I/O information is, however, valid at the leading edge of ALE and can be latched externally using this signal if necessary.

2.4.2Disabling Internal Program Memory

Applying +5V to the EA (external access) pin of the MCS-48 microcomputers allows the user to effectively disable internal program memory by forcing all instruction fetches to occur from an external memory. This external memory can be connected as explained in the section on program memory expansion and can contain a diagnostic routine to exercise the processor, the internal RAM, the timer, and the I/O lines. EA should be switched only when the processor is in

RESET.

2.4.3Reading Internal Prograin Memory

Just as the processor may be isolated from internal program memory using EA, program memory can be read independent of the processor using the verification mode des- cribed in the previous section, Programming/ Verification.

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