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Semiconductor Group
45
On-Chip Peripheral Components
7.1.4.2 Port Loading and Interfacing
The output buffers of ports 1 through 5 can drive TTL inputs directly. The maximum port load which
still guarantees correct logic output levels can belooked up in the DC characteristics in the Data
Sheet of the SAB 80(C)515. The corresponding parameters are
V
OL
and
V
OH
.
The same applies to port 0 output buffers. They do, however, require external pullups to drive
floating inputs, except when being used as the address/data bus.
When used as inputs it must be noted that the ports 1 through 5 are not floating but have internal
pullup transistors. The driving devices must be capable of sinking a sufficient current if a logic low
level shall be applied to the port pin (the parameters
I
TL
and
I
IL
in the DC characteristics specify
these currents). Port 0 as well as the input only ports 6 of the ACMOS versions have floating inputs
when used for digital input.
7.1.4.3 Read-Modify-Write Feature of Ports 0 through 5
Some port-reading instructions read the latch and others read the pin (see figure 7-1). The
instructions reading the latch rather than the pin read a value, possibly change it, and then rewrite
it to the latch. These are called "read-modify-write" instructions, which are listed in table 7-2. lf the
destination is a port or a port bit, these instructions read the latch rather than the pin. Note that all
other instructions which can be used to read a port, exclusively read the port pin. In any case,
reading from latch or pin, resp., is performed by reading the SFR P0 to P5; for example,
"MOV A, P3" reads the value from port 3 pins, while "ANL P4, #0AAH" reads from the latch,
modifies the value and writes it back to the latch.
*
Summary of Contents for SAB 80515 Series
Page 9: ...Semiconductor Group 9 Introduction Figure 1 2 Block Diagram ...
Page 12: ...Semiconductor Group 12 Fundamental Structure Figure 2 1 Detailed Block Diagram ...
Page 18: ...Semiconductor Group 18 Central Processing Unit Figure 3 1 Fetch Execute Sequence ...
Page 73: ...Semiconductor Group 73 On Chip Peripheral Components Figure 7 25 A D Converter Block Diagram ...
Page 83: ...Semiconductor Group 83 On Chip Peripheral Components Figure 7 33 a Timer 2 Block Diagram ...
Page 215: ...Device Specifications Semiconductor Group 215 ...
Page 217: ...Device Specifications Semiconductor Group 217 Pin Configuration P LCC 68 ...
Page 219: ...Device Specifications Semiconductor Group 219 Logic Symbol ...
Page 226: ...Device Specifications Semiconductor Group 226 Figure 1 Block Diagram ...
Page 229: ...Device Specifications Semiconductor Group 229 Figure 2 Memory Address Spaces ...
Page 239: ...Device Specifications Semiconductor Group 239 Figure 4 Block Diagram of the A D Converter ...
Page 241: ...Device Specifications Semiconductor Group 241 Figure 5 Interrupt Request Sources ...
Page 242: ...Device Specifications Semiconductor Group 242 Figure 6 Interrupt Priority Level Structure ...