P80C42 datasheet(6/25 Pages) INTEL

Part #	P80C42

Description	UNIVERSAL PERIPHERAL INTERFACE CHMOS 8-BIT SLAVE MICROCONTROLLER

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Manufacturer	INTEL [Intel Corporation]

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UPI-C42UPI-L42

If ‘‘EN DMA’’ has been executed P27 becomes

the DACK (DMA ACKnowledge) pin This pin acts

as a chip select input for the Data Bus Buffer

registers during DMA transfers

EN DMA

Op Code 0E5H

1

110010

1

D7

D0

6

When EA is enabled on the UPI the program

counter is placed on Port 1 and the lower four

bits of Port 2 (MSB e P23 LSB e P10) On the

UPI this information is multiplexed with PORT

DATA (see port timing diagrams at end of this

data sheet)

7

The UPI-C42 supports the Quick Pulse Program-

ming Algorithm but can also be programmed

with the Intelligent Programming Algorithm (See

the Programming Section)

UPI-C42 FEATURES

Programmable Memory Size Increase

The user programmable memory on the UPI-C42 will

be increased from the 2K available in the NMOS

product by 2X to 4K The larger user programmable

memory array will allow the user to develop more

complex peripheral control micro-code P23 (port 2

bit 3) has been designated as the extra address pin

required to support the programming of the extra 2K

of user programmable memory

The new instruction SEL PMB1 (73h) allows for ac-

cess to the upper 2K bank (locations 2048 – 4095)

The additional memory is completely transparent to

users not wishing to take advantage of the extra

memory space No new commands are required to

access the lower 2K bytes The SEL PMB0 (63h)

has also been added to the UPI-C42 instruction set

to allow for switching between memory banks

Extended Memory Program

Addressing (Beyond 2K)

For programs of 2K words or less the UPI-C42 ad-

dresses program memory in the conventional man-

ner Addresses beyond 2047 can be reached by ex-

ecuting a program memory bank switch instruction

(SEL PMB0 SEL PMB1) followed by a branch in-

struction (JMP or CALL) The bank switch feature

extends the range of branch instructions beyond

their normal 2K range and at the same time prevents

the user from inadvertently crossing the 2K boundary

PROGRAM MEMORY BANK SWITCH

The switching of 2K program memory banks is ac-

complished by directly setting or resetting the most

significant bit of the program counter (bit 11) see

Figure 5 Bit 11 is not altered by normal increment-

ing of the program counter but is loaded with the

contents of a special flip-flop each time a JMP or

CALL instruction is executed This special flip-flop is

set by executing an SEL PMB1 instruction and reset

by SEL PMB0 Therefore the SEL PMB instruction

may be executed at any time prior to the actual bank

switch which occurs during the next branch instruc-

tion encountered Since all twelve bits of the pro-

gram counter including bit 11 are stored in the

stack when a Call is executed the user may jump to

subroutines across the 2K boundary and the proper

PC will be restored upon return However the bank

switch flip-flop will not be altered on return

290414 – 30

Figure 5 Program Counter

INTERRUPT ROUTINES

Interrupts always vector the program counter to lo-

cation 3 or 7 in the first 2K bank and bit 11 of the

program counter is held at ‘‘0’’ during the interrupt

service routine The end of the service routine is sig-

naled by the execution of an RETR instruction Inter-

rupt service routines should therefore be contained

entirely in the lower 2K words of program memory

The execution of a SEL PMB0 or SEL PMB1 instruc-

tion within an interrupt routine is not recommended

since it will not alter PC11 while in the routine but

will change the internal flip-flop

Hardware A20 Gate Support

This feature has been provided to enhance the per-

formance of the UPI-C42 when being used in a key-

board controller application The UPI-C42 design

has included on chip logic to support a hardware

GATEA20 feature which eliminates the need to pro-

vide firmware to process A20 command sequences

6

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