80C575 Datasheet, PDF(22/40 Page) NXP Semiconductors – 80C51 8-bit microcontroller family 8K/256 OTP/ROM/ROMless, 4 comparator, failure detect circuitry, watchdog timer

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80C575 Datasheet, PDF (22/40 Pages) NXP Semiconductors – 80C51 8-bit microcontroller family 8K/256 OTP/ROM/ROMless, 4 comparator, failure detect circuitry, watchdog timer

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Philips Semiconductors

80C51 8-bit microcontroller family

8K/256 OTP/ROM/ROMless, 4 comparator, failure detect circuitry, watchdog timer

Product specification

80C575/83C575/

87C575

SM0

SM1

SM2

REN

TB8

RB8

SCON

(98H)

RECEIVED ADDRESS D0 TO D7

PROGRAMMED ADDRESS

COMPARATOR

IN UART MODE 2 OR MODE 3 AND SM2 = 1:

INTERRUPT IF REN=1, RB8=1 AND âRECEIVED ADDRESSâ = âPROGRAMMED ADDRESSâ

â WHEN OWN ADDRESS RECEIVED, CLEAR SM2 TO RECEIVE DATA BYTES

â WHEN ALL DATA BYTES HAVE BEEN RECEIVED: SET SM2 TO WAIT FOR NEXT ADDRESS.

Figure 20. UART Multiprocessor Communication, Automatic Address Recognition

SU00045

CMP Register Bit Definitions

CMP.7 enable comparator 3,

disable pullups at P3.4, P3.7

CMP.6 enable comparator 2,

disable pullups at P3.4, P3.6

CMP.5 enable comparator 1,

disable pullups at P3.4, P3.5

CMP.4 enable comparator 0,

disable pullups at P1.0, P1.1

CMP.3 comparator 3 output (read only)

CMP.2 comparator 2 output (read only)

CMP.1 comparator 1 output (read only)

CMP.0 comparator 0 output (read only)

All comparators are disabled automatically in

power down mode, in idle mode unused

comparators should be disabled by software

to save power. A comparator can generate

an interrupt that will terminate idle mode.

The CMPE register contains bits to enable

each comparator to drive external output pins

or internal PCA capture inputs. Pullups at the

output pins are disabled by hardware when

the external comparator output is enabled.

The comparator output is wire-ORed with the

corresponding port SFR bit, so the SFR bit

must also be set by software to enable the

output.

CMPE Register Bit Definitions

CMPE.7 enables comparator 3 to drive

CEX3

CMPE.6 enables comparator 2 to drive

CEX2

CMPE.5 enables comparator 1 to drive

CEX1

CMPE.4 enables comparator 0 to drive

CEX0

CMPE.3 enables comparator 3 output on

P1.6 (open drain)

CMPE.2 enables comparator 2 output on

P1.5 (open drain)

CMPE.1 enables comparator 1 output on

P1.4 (open drain)

CMPE.0 enables comparator 0 output on

P1.3 (open drain)

When 1s are written to CMPE bits 7-4,

the comparator outputs will drive the

corresponding capture input. (This function is

not available in the idle or power-down

mode.) When 1s are written to CMPE bits 3-0

the comparator output will also drive the

corresponding port 1 pin. (This function is

available in idle mode.) If the comparatorâs

enabled to drive the capture input but not the

port pin, then the port pin can be used for

general purpose I/O. When a comparator

output is enabled, pullups at the output pin

are disabled and the output becomes open

drain. The comparator output can be used to

trigger a capture input in idle mode by

programming the CMPE register to drive the

pin from the comparator output to have the

pin supply the capture trigger.

There are two special function registers

associated with the comparators. They are

CMP which contains the comparator enables

and a bit that can be read by software to

determine the state of each comparatorâs

output, and CMPE which controls whether

the output from each comparator drives the

associated output pin or a capture input

associated with one of the PCA modules.

The CMP registers bits 0â3 can be read by

software to determine the state of the output

of each comparator. To do this the associated

comparator must be enabled but the output in

port 1 can be disabled. This allows easy

polling of the comparator output value without

the need to use up a port pin.

The CMPE register allows the comparator to

drive the associated PCA module capture

input, so that on compare a capture can be

generated in the PCA. Bits 0â3 of this

the associated port 1 output circuitry. Used

as a comparator output this circuitry is open

drain. To enable the comparator output to

drive to port 1, the corresponding port bit

must also be set to disable the pulldown. If

the comparator is not enabled to drive the

port 1 circuitry, the associated port 1 pin can

be used for other I/O. This includes when a

comparator is enabled to drive the capture

input to a PCA module.

1998 May 01

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