MCS(R) 51 FX/GX Microcontoller New Interrupt Priority Register

ABSTRACT:

This TechBit clarifies the name and function of the new
interrupt priority register on the FX core.

NEW INTERRUPT PRIORITY REGISTER NAME

There has been some confusion about the name and function
of the new interrupt priority register resident on the FX
core.

Figure 1 shows the correct naming convention for the
register.

____________________________________________________
|IPH | | | | | | | |
|(0B7H)| - |PPCH |PT2H |PSH | PT1H | PX1H | PT0H | PX0H
|______|____|_____|_____|_____|______|______|_____|

Figure 1

The new register becomes the MSB of the priority select
bits and the existing IP register acts as the LSB. This
scheme maintains compatibility with the rest of the MCS-51
family.

Table 1 shows the bit values and the priority level
associated with each combination.

Priority Select Bits
MSB LSB

IPH.X	IP.X	(X is the bit position 0 - 6)
0	0	Interrupt Priority level 0 (lowest)
0	1	Interrupt Priority level 1
1	0	Interrupt Priority level 2
1	1	Interrupt Priority level 3 (highest)

Table 1

To assure that all publications describing this feature
are in complete agreement, an Automotive Handbook errata list
is outlined below for the 87C51GB.

Interrupt Priority Register as seen in the 1989
Automotive Handbook.

7 6 5 4 3 2 1 0

IP (OB8H) - PC PT2 PS PT1 PX1 PT0 PX0

IP1 (0B7H) - PC_1 PT2_1 PS_1 PT1_1 PX1_1 PT0_1 PX0_1

Interrupt Priority Register as seen in the 1990
Automotive Handbook.

7 6 5 4 3 2 1 0

IP (0B8H) - PC PT2 PS PT1 PX1 PT0 PX0

IPL (0B7H) - PCL PT2L PSL PT1L PX1L PT0L PX0L

Correct Interrupt Priority Register for the 1990
Automotive Handbook.

7 6 5 4 3 2 1 0

IP (0B8H) - PC PT2 PS PT1 PX1 PT0 PX0

IPH (0B7H) - PPCH PT2H PSH PT1H PX1H PT0H PX0H

The IP1 bit functions defined at the bottom of the
Interrupt Priority Register Table should also be changed to
match the IPH (0B7H) names from above.

PC_1 should be PCCH
PC2_1 should be PT2H
PS_1 should be PSH
PT1_1 should be PT1H
PX1_1 should be PX1H
PT0_1 should be PT0H
PX0_1 should be PX0H

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