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10.3
R Ports
10.3.1
Overview
The R port consists of the six 4-bit I/O ports R0 to R4 and R8 and the 1-bit input port RA
1. These
ports are accessed in 4-bit units.
R0, R1, R3, R4, and R8 are standard voltage CMOS three state I/O ports and R2 is a medium
voltage NMOS open drain I/O port of HD404358 Series.
On the HD404358R series pins R0, R1, R2, R3, R4, and R8 are CMOS three state standard
voltage I/O pins. Of these, R0, R1, R2, and R8 can handle high current levels of up to 15 mA.
The individual ports R0 to R4 and R8 are accessed in 4-bit units with the LRA and LRB output
instructions to control the output levels (high or low) on each pin. Output data is stored in the PDR
built into each pin. Similarly, the LAR and LBR input instructions can be used to access the R
ports in 4-bit units to read the input levels on the port pins.
The RA1 input-only port consists of a single bit. The values of bits 3, 2, and 0 are undefined when
this port is accessed by the input instructions.
DCR registers are used to control on/off states of the R port output buffers. When the DCR bit
corresponding to a pin in an R port is set to 1, the contents of the PDR corresponding to that pin is
output from the pin. Thus the output buffer on/off states can be controlled on an individual pin
basis for the R port pins. The DCR registers are allocated in the RAM address space.
The R0, R3, and R4 port pins have shared functions as built-in peripheral module pins. Register
settings are used to switch these functions. (See table 10-8.)
Figure 10-2 shows the R port pin structure.