SM1126 Series

NIPPON PRECISION CIRCUITS—7

Serial inputs

Serial data is input on SIO in sync with the SC clock in 8-bit units when ST is LOW. Data is not accepted

when ST is HIGH. When ST goes HIGH, the 8-bit data is latched. Note that if the input data exceeds 8 bits in

length, the most recent 8 bits are used and any preceding bits are ignored. Data is in MSB first format.

Input data is interpreted as a command or as a data word (in write mode), depending on the current operating

mode of the device. There are 3 types of commands:

s

Playback start command

s

SRAM write command

s

End-of-write command

The SRAM write command is used to invoke write mode operation, and end-of-write command is used to

return to play mode operation. In write mode, however, data is interpreted as data words to be written to

SRAM.

Note that pin SIO is an output pin only when the parity check command is executed. At all other times, SIO

is an input pin.

Playback control

The ST pin controls the start of playback. While ST is HIGH, the melody is played repeatedly, and when ST

goes LOW, playback stops. Melodies are selected by input serial data on pins SIO and SC, as shown in table 2.

The melody select command comprises a fixed code (1000) followed by 4 melody select data bits (B3 to B0).

The 8 bits of data are retained even after playback. If serial data is input during playback, the data is ignored

and playback continues.

Pin SC should be LOW when either a LOW-to-HIGH or HIGH-to-LOW transition occurs on pin ST.

Figure 4. Serial input timing

Pin SC should be LOW when either a LOW-to-HIGH or HIGH-to-LOW transition occurs on pin ST.

Figure 5. Serial data input timing

SIO

SC

ST

Invalid

Data

Invalid

Data

?

?

B3 B2 B1 B0

B7 B6 B5 B4

?

?

?

?

?

?

?

?

?

?

Valid

Data

SIO

SC

ST

MTO

Invalid

Data

Invalid

Data

?

?

B3 B2 B1 B0

HL LL

?

?

?

?

?

?

?

?

?

?

Valid

Data