Ram Self-Check Subroutine; Rom Checksum Subroutine; Analog-To-Digital Converter Self-Check - Motorola MC6805R Series Advance Information

SECTION 6
SELF-CHECK
The self-check capability of the MC6805R2, MC6805U2, MC6805R3, and MC6805U3 microcom-
puters provides an internal check to determine if the part is functional. Connect the MCU as shown
in Figure 6-1 and monitor the output of port C bit 3 for an oscillation of approximately 7 hertz. A
1O-volt level (through a 10k resistor) on the timer input, pin 8, and pressing then releasing the
RESE'F
button, energizes the ROM-based self-check feature. The self-check program exercises the
RAM, ROM, TIMER, interrupts, and 1/0 ports, as well as the AID for the MC6805R2 and
MC6805R3.
Several of the self-check subroutines can be called by a user program with a JSR or BSR instruc-
tion. They are the RAM, ROM, and four-channel AID tests. The timer routine may also be called if
the timer input is the internal phase two clock.
6.1 RAM SELF-CHECK SUBROUTINE
The RAM self-check is called at location $F6F for the MC6805R2/MC6805U2 and at location $F84
for the MC6805R3/MC6805U3. If any error is detected, it returns with the Z bit cleared;. otherwise
the Z bit is set. The walking diagnostic pattern method is used on the MC6805R2/U2. The
MC6805R3/U3 test causes each byte to count from 0 up to 0 again with
a
check after each count.
The RAM test must be called with the stack pointer at $07F. When run, the test checks every RAM
cell except for $07F and $07E which are assumed to contain the return address.
The A and X registers and all RAM locations except $07F and $07E are modified.
6.2 ROM CHECKSUM SUBROUTINE
The ROM self-check is called at location $F8A for the MC6805R2/MC6805U2 and at location $F95
for the MC6805R3/MC6805U3.
The A register should be cleared before calling the routine in the MC6805R3/MC6805U3. If any
error is detected, it retu rns with the Z bit cleared; otherwise Z
=
1, X
=
0 on retu rn, and A is zero if
the test passes. RAM location $040 is overwritten.
6.3 ANALOG-TO-OIGITAL CONVERTER SELF-CHECK
The analog-to-digital self-check for the MC6805R2 is called at location $FA4 and for the MC6805R3
at $FAE. For both devices; it returns with the
Z
bit cleared if any error was found; otherwise the
Z
bit is set.
6-1