AT89LP51 datasheet(80/113 Pages) ATMEL

80 / 113 page

3709C–MICRO–5/11

AT89LP51/52 - Preliminary

The Parallel interface is a special mode of the serial interface, i.e. the serial interface is used to

enable the parallel interface. After enabling the interface serially over P1.7/SCK and P1.5/MOSI,

P1.5 is reconfigured as an active-low output enable (OE) for data on Port 0. When OE =1, com-

mand, address and write data bytes are input on Port 0 and sampled at the rising edge of SCK.

When OE =0, read data bytes are output on Port 0 and should be sampled on the falling edge of

SCK. The P1.7/SCK and RST pins continue to function in the same manner. With the addition of

VDD and GND, the parallel interface requires a minimum of fourteen connections as shown in

Figure 17-2. Note that a connection to P1.6/MISO is not required for using the parallel interface.

Figure 17-2. Parallel Programming Device Connections

The Programming Interface is the only means of externally programming the AT89LP51/52

microcontroller. The Interface can be used to program the device both in-system and in a stand-

alone serial programmer. The Interface does not require any clock other than SCK and is not

limited by the system clock frequency. During Programming the system clock source of the tar-

get device can operate normally.

When designing a system where In-System Programming will be used, the following observa-

tions must be considered for correct operation:

•The ISP interface uses the SPI clock mode 0 (CPOL = 0, CPHA = 0) exclusively with a

maximum frequency of 5 MHz.

•The AT89LP51/52 will enter programming mode only when its reset line (RST) is active. To

simplify this operation, it is recommended that the target reset can be controlled by the In-

System programmer. To avoid problems, the In-System programmer should be able to keep

the entire target system reset for the duration of the programming cycle. The target system

should never attempt to drive the three SPI lines while reset is active.

•The ISP Enable Fuse must be set to allow programming during any reset period. If the ISP

Fuse is disabled, ISP may only be entered at POR. To enter programming the RST pin must

be driven active prior to the end of Power-On Reset (POR). After POR has completed the

device will remain in ISP mode until RST is brought inactive. Once the initial ISP session has

ended, the power to the target device must be cycled OFF and ON to enter another session.

Note that if this method is required, an active-low reset polarity is recommended.

•For standalone programmers, an active-low reset polarity is recommended (POL = 0). RST

may then be tied directly to GND to ensure correct entry into Programming mode regardless

of the device settings.

AT89LP51/52

VDD

RST

P1.7/SCK

P1.5/MOSI

GND

Clock

RST

POL

GND or VDD

P0.7-0

Data In/Out

AT89LP51 数据表(PDF) 80 Page - ATMEL Corporation

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