NEC switch - Manual (Page 63)

CHAPTER 4 PORT FUNCTIONS
User’s Manual U12978EJ3V0UD
63
Figure 4-5. Block Diagram of P21
PU0: Pull-up resistor option register 0
PM: Port mode register
RD: Port 2 read signal
WR: Port 2 write signal
Internal bus
V DD0
P-ch
P21/SO10
WR
PU0
RD
WR
PORT
WR PM
PU02
Output latch
(P21)
PM21
Alternate
function
Selector