CHAPTER 5 PORT FUNCTIONS
Page 86 of 920
5.4.4
Handling different potential (1.8 V, 2.5 V, 3 V) by using I/O buffers
It is possible to connect an external device operating on a different potential (1.8 V, 2.5 V, or 3 V) by switching I/O
buffers with the port input mode register (PIMxx) and port output mode register (POMxx).
When receiving input from an external device with a different potential (1.8 V, 2.5 V, or 3 V), set the port input
mode registers 0, 8, and 14 (PIM0, PIM8, and PIM14) on a bit-by-bit basis to enable normal input (CMOS)/TTL
input buffer switching.
When outputting data to an external device with a different potential (1.8 V, 2.5 V, or 3 V), set the port output
mode registers 0, 7, 8, and 14 (POM0, POM7, POM8, and POM14) on a bit-by-bit basis to enable normal output
(CMOS)/N-ch open drain (V
DD
tolerance) switching.
The connection of a serial interface is described in the following.
(1) Setting procedure when using input pins of UART1, UART3, CSI10, and CSI30 functions for the TTL input
buffer
In case of UART1:
P03
In case of UART3:
P143
In case of CSI10:
P03, P04
In case of CSI30:
P142, P143
<1> Using an external resistor, pull up the pin to be used to the power supply of the target device (on-chip
pull-up resistor cannot be used).
<2> Set the corresponding bit of the PIM0 and PIM14 registers to 1 to switch to the TTL input buffer. For
V
IH
and V
IL
, refer to the DC characteristics when the TTL input buffer is selected.
<3> Enable the operation of the serial array unit and set the mode to the UART/CSI mode.
(2) Setting procedure when using output pins of UART1, UART3, CSI10, and CSI30 functions in N-ch open-
drain output mode
In case of UART1:
P02
In case of UART3:
P144
In case of CSI10:
P02, P04
In case of CSI30:
P142, P144
<1> Using an external resistor, pull up the pin to be used to the power supply of the target device (on-chip
pull-up resistor cannot be used).
<2> After reset release, the port mode is the input mode (Hi-Z).
<3> Set the output latch of the corresponding port to 1.
<4> Set the corresponding bit of the POM0 and POM14 registers to 1 to set the N-ch open drain output
(V
DD
tolerance) mode.
<5> Enable the operation of the serial array unit and set the mode to the UART/CSI mode.
<6> Set the corresponding bit of the PM0 and PM14 registers to the output mode. At this time, the output
data is high level, so the pin is in the Hi-Z state.
Содержание RL78/G1H
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