ST7556 Sitronix Technology, ST7556 Datasheet - Page 16

• Manufacturer Part Number: ST7556
• Description: 65 x 102 Dot Matrix LCD Controller/Driver
• Manufacturer: Sitronix Technology

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ST7556
Busy Flag
The Busy Flag indicates whether the ST7556 is operating or not. When D7 is "H" in read status operation, this device is in
busy status and will accept only read status instruction. If the cycle time is correct, the microprocessor needs not to check
this flag before each instruction, which improves the MPU performance.
Data Transfer
The ST7556 uses bus holder and internal data bus for data transfer with the MPU. When writing data from the MPU to
on-chip RAM, data is automatically transferred from the bus holder to the RAM as shown in figure 3. And when reading
data from on-chip RAM to the MPU, the data for the initial read cycle is stored in the bus holder (dummy read) and the MPU
reads this stored data from bus holder for the next data read cycle as shown in figure 4. This means that a dummy read
cycle must be inserted between each pair of address sets when a sequence of address sets is executed. Therefore, the
data of the specified address cannot be output with the read display data instruction right after the address sets, but can be
output at the second read of data.
Ver 2.2
COLUMN ADDRESS
BUS HOLDER
D0 to D7
Internal signals
CSB
SCL
A0
MPU signal
/WR
/WR
SI
A0
N
N
Fig 3. Write Timing
DB7
Fig 2. 4-line SPI Timing
D(N)
D(N)
N
DB6
DB5
N+1
D(N+1) D(N+2)
D(N+1)
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DB4
N+2
D(N+2)
DB3
DB2
N+3
D(N+3)
D(N+3)
DB1
DB0
DB7
DB6
2005/10/05