ST7920
Parallel interface:
ST7920 is in parallel mode by pulling up PSB pin. ST7920 can select 8-bit or 4-bit bus interface by setting the DL
control bit in “Function Set” instruction. MPU can control RS, RW, E and DB0…DB7 pins to complete the data
transmission.
In 4-bit transfer mode, every 8-bit data or instruction is separated into 2 parts. The higher 4 bits (bit-7~bit-4) data will
be transfered first through data pins (DB7~DB4). The lower 4 bits (bit-3~bit-0) data will be transfered second through
data pins (DB7~DB4). The (DB3~DB0) data pins are not used during 4-bit transfer mode.
RS
RW
E
DB0-DB7
Instruction write
Dummy read RAM read
Timing Diagram of 8-bit Parallel Bus Mode Data Transfer
RS
RW
E
Upper
4-bit
Lower
4-bit
Upper
4-bit
Lower
4-bit
Upper
4-bit
Lower
4-bit
DB0-DB7
Instruction write
Dummy read
RAM read
Timing Diagram of 4-bit Parallel Bus Mode Data Transfer
V4.0
25/49
2008/08/18
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