Siemens S50037 USB Timing, Serial Peripheral Interface, Instruction Cycle, Single-Cycle Operation

SieMo S50037 Data Book PRELIMINARILY

figure 20 USB Power Modes- Applications

USB Timing

figure 21 USB Disconnect and Resume Signal Timing

Serial Peripheral Interface

Overview

￿Consistent with the Motorola SPI standard

￿SieMo always acts in slave mode

￿SPI_CLK is always generated by the host

SieMo uses 16-bit addresses and 16-bit data during serial peripheral interface transactions. Such transactions will operate regardless of whether the internal processor is running or is stopped. This section details the considerations required when interfacing to SieMo via the four dedicated Serial peripheral interface terminals.

Instruction Cycle

Before SieMo can be addressed, SPI_CSB must be taken low (SPI_CSB = 0). Data on SPI_MOSI is then clocked into the SieMo on the rising edge of the clock-line SPI_CLK. When reading, SieMo will reply to the master on MISO, the data being valid on the falling edge of the SPI_CLK. The master provides the clocking.

Single-Cycle Operation

After a serial peripheral interface transaction finishes, the master toggles SPI_CLK with

SPI_CSB high to initiate a new transaction. SPI_CSB must be high for at least two SPI_CLK cycles.

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