Keyboard Circuit; Keyboard Block Diagram - Sam4s ER-5200 Service Manual

7-6 Keyboard Circuit

The Key Board Circuit consist of the scan signal of 20 lines and the return signal of 8-line. The CPU sends repeatedly and
continuously the scan data S0 S
signal if the specific key is pressed during the given time. The CPU reads the data through U27(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 U27(74HC541) and performs the
selected function.
ADDRESS DECODER
COMMON PORT
SAM4S ER-5200 Series
∼ 19 through the 74HCT138(U16,U18,U23). The key information input in the return
CS1, ADDR[11:13], nRESET
(74HC138,U21)
KBD_CS
ADDRESS DECODER(74HC138)
( U16, U18, U23 )
DIODE( MMBD6050L *20)
160 KEYS
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Figure 7-13 Keyboard Block Diagram
CPU (M30800SFP)
ADDR[0:5]
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MODE KEY
7 Special Circuit Description
DATA[0:7]
Pull-Up
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74HCT541
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(U27)
7-9