30-4
MC9328MX1 Reference Manual
MOTOROLA
Synchronous Serial Interface (SSI)
30.2.1 SSI Clocking
The SSI uses the following clocks:
•
Serial bit clock—Serially clocks the data bits in and out of the SSI port
•
Word clock—Counts the number of data bits per word (8, 10, 12, or 16 bits)
•
Frame clock—Counts the number of words in a frame
•
SYS_CLK—Input Clock from the PLL Clock Controller Module (PerCLK3). Made available on
an output pin in synchronous master mode.
30.2.1.1 Normal Operating Mode
In normal operating mode, when the I
2
S Mode Select bits (I2S_MODE1 and I2S_MODE0) in the SSI
Control/Status Register (SCSR) are both clear, the serial bit clock is available on the serial transmit
clock (SSI_TXCLK) and serial receive clock (SSI_RXCLK) pins. The word clock is an internal clock that
determines when transmission of an 8-, 10-, 12-, or 16-bit word is complete. The word clock also clocks
the frame clock, which counts the number of words in the frame. The frame sync clock is available on the
SSI_TXFS and SSI_RXFS frame sync pins because a frame sync is generated after the correct number of
words in the frame are transmitted/received. See Section 30.5, “SSI Operating Modes,” on page 30-38 for
a detail description about the SSI operating modes.
30.2.1.2 Master / Synchronous Mode
In master mode and synchronous mode, the unused SSI_RXCLK pin outputs the serial system
clock (SYS_CLK) enabled by the SYS_CLK_EN bit in the SSI Control/Status Register (SCSR). The
SYS_CLK (PerCLK3) is the input clock into the SSI module. The SSI Clock Generator uses the word
length (WL), prescaler range (PSR), prescaler modulus select (PM), and frame rate divider control (DC) to
generate the other clocks from SYS_CLK (PerCLK3). The relationship between the clocks and the
dividers is shown in Figure 30-3. A serial bit clock may be received from a SSI clock pin or can be
generated internally from the PerCLK3 clock by a series of dividers, as shown in Figure 30-4.
Figure 30-3. SSI Clocking
30.2.2 SSI Clock and Frame Sync Generation
Data clock and frame sync signals are generated internally by the MC9328MX1 or can be obtained from
external sources. When generated internally, the SSI clock generator derives bit clock and frame sync
signals from an input clock signal. The SSI clock generator consists of a selectable, fixed prescaler and a
programmable prescaler for bit rate clock generation. In gated clock mode, the data clock is valid only
when data is being transmitted. If the pull-up is disabled for this pin in the GPIO Module’s Pull-Up Enable
Register, then the clock pin is tri-stated when data is not transmitting.
A programmable frame rate divider and a word length divider are used for frame rate sync signal
generation.
Figure 30-4 on page 30-5 shows a block diagram of the clock generator for the transmit section. Whether
the serial bit clock is generated internally or derived from an external source depends on the transmit
direction (
Word Divider
(÷8, ÷10, ÷12, ÷16)
Frame Divider
(÷1, to ÷32)
Serial Bit Clock
Word Clock
Frame Clock
Summary of Contents for DragonBall MC9328MX1
Page 68: ...1 12 MC9328MX1 Reference Manual MOTOROLA Introduction ...
Page 86: ...2 18 MC9328MX1 Reference Manual MOTOROLA Signal Descriptions and Pin Assignments ...
Page 116: ...3 30 MC9328MX1 Reference Manual MOTOROLA Memory Map ...
Page 126: ...4 10 MC9328MX1 Reference Manual MOTOROLA ARM920T Processor ...
Page 160: ...8 8 MC9328MX1 Reference Manual MOTOROLA System Control ...
Page 272: ...13 32 MC9328MX1 Reference Manual MOTOROLA DMA Controller ...
Page 281: ...Programming Model MOTOROLA Watchdog Timer Module 14 9 ...
Page 282: ...14 10 MC9328MX1 Reference Manual MOTOROLA Watchdog Timer Module ...
Page 300: ...15 18 MC9328MX1 Reference Manual MOTOROLA Analog Signal Processor ASP ...
Page 438: ...18 16 MC9328MX1 Reference Manual MOTOROLA Serial Peripheral Interface Modules SPI 1 and SPI 2 ...
Page 478: ...19 40 MC9328MX1 Reference Manual MOTOROLA LCD Controller ...
Page 574: ...21 32 MC9328MX1 Reference Manual MOTOROLA Memory Stick Host Controller MSHC Module ...
Page 598: ...23 16 MC9328MX1 Reference Manual MOTOROLA Real Time Clock RTC ...
Page 670: ...24 72 MC9328MX1 Reference Manual MOTOROLA SDRAM Memory Controller ...
Page 726: ...25 56 MC9328MX1 Reference Manual MOTOROLA SmartCard Interface Module SIM ...
Page 736: ...26 10 MC9328MX1 Reference Manual MOTOROLA General Purpose Timers ...
Page 854: ...29 18 MC9328MX1 Reference Manual MOTOROLA I2C Module ...
Page 900: ...30 46 MC9328MX1 Reference Manual MOTOROLA Synchronous Serial Interface SSI ...
Page 942: ...32 26 MC9328MX1 Reference Manual MOTOROLA GPIO Module and I O Multiplexer IOMUX ...