Sam4s ER-380F - Keyboard Circuit

7 Special Circuit Descriptions
7-6 SAM4S ER-380M/F SERIES
7-4 Keyboard Circuit
The Key Board Circuit consist of the scan signal of 8 lines and the return signal of 8-line. The CPU sends repeatedly and
continuously the scan data S0 S∼ 7 through the 74HCT138(U21). The key information input in the return signal if the
specific key is pressed during the given time. The CPU reads the data through U23(74HC541) and analyzes what key is
pressed and transmits this information to the CPU, then performs the selected function. The Key Board Circuit sends the
mode scan signal to the Key-lock switch and takes the return data through the U23(74HC541) and performs the selected
function.
Figure 7-8 Keyboard Block Diagram
DATA[0:7]
74HCT541
(U23)
ADDR[0:3]
CPU (M30800SFP)
44 KEYS
Pull-Up
COMMON PORT
•
•
•
•
•
•
•
MODE KEY
•
•
•
•
•
•
•
•
ADDRESS DECODER(74HC138)
( U21 )
DIODE( MMBD6050L *8)
P10.3