Intel SA-1100 manual External Clock Operation, Alternate SSP Pin Assignment

Peripheral Control Module

A register read is performed by writing a value to MCP data register 2 that contains the address of the register and the read/write bit set to a zero. Again, the data is transferred to the serial shifter on the next rising edge of the SFRM signal and is transmitted to the UCB1100 or UCB1200 during subframe 0. Because the address and read/write control bit fields occur near the beginning of the serial stream output, the codec performs the read immediately after the read/write bit is received (during the 41st bit of the frame) and the value contained within the addressed register is sent back to the MCP in the same data frame.

Once the codec control register is written with a value to execute a read or write, the operation is performed every MCP data frame until a new value is written to the register. Thus, continual reads or writes are made to the addressed codec register until a new read or write operation is configured.

11.12.1.5External Clock Operation

Under normal operation, the MCP is programmed to use one of two on-chip clocks to produce a 9.585-Mbps or 11.981-Mbps bit rate. This clock is also used to increment the audio and telecom sample rate counters. The MCP also supports a special mode that allows the user to control the MCP’s frame rate and audio/telecom sample rates. This mode is useful when sample rates that are not an integer multiple of 12 MHz are required. In this mode, the MCP uses GPIO<21> to input a clock supplied from off-chip. The frequency of the off-chip clock can be any value within the allowable frequency range of the UCB100, up to 12 MHz. When using GPIO pin 21 for the input clock, the user must also set bit 21 of the GPIO alternate function register (GAFR) and clear bit 21 of the GPIO pin direction register (GPDR). See the Section 9.1, “General-Purpose I/O” on

page 9-1.

11.12.1.6Alternate SSP Pin Assignment

MCP operation takes precedence over SSP operation. Thus if both are enabled, serial port 4 defaults to MCP mode. However, if the MCP and SSP both need to be used at the same time, general-purpose I/O pins 10..13 (GPIO<10..13>) can be reassigned by programming the PPC pin assignment register (PPAR). This allows the MCP dedicated use of the four pins assigned to serial port 4, and the SSP dedicated use of the GPIO pins. When the SSP pin reassignment (SPR) bit is set in PPAR, the following pin assignments are made: GPIO<10> is used for transmit, GPIO<11> for receive, GPIO<12> for serial clock, and GPIO<13> for serial frame. Note that the user must also set bits 10 through 13 in the GPIO alternate function register (GAFR) as well as set bits 10, 12, and 13, and clear bit 11 in the GPIO pin direction register (GPDR). Once the reassignment is made, these pins are no longer usable by the GPIO unit. See the Section 9.1, “General-Purpose I/O” on page 9-1for a description of how to program the system control module and the Section 11.13, “Peripheral Pin Controller (PPC)” on page 11-184for a description of how to program the PPC unit.

11.12.1.7CPU and DMA Register Access Sizes

Bit positioning and addressing of the MCP is described in terms of little endian ordering. All MCP registers are 32 bits wide. The ARM peripheral bus does not support byte or half-word operations. All reads and writes of the MCP by the CPU should be wordwide. Four separate dedicated DMA requests exist for the audio and telecom transmit and receive FIFOs. If the DMA controller is used to service the transmit and/or receive FIFOs, the user must ensure the DMA is properly configured to perform half-word accesses, using 4 half-words per burst (half the size of the FIFOs). Note that a separate set of registers also exist to configure SSP operation. See the following sections for a full description of programming and operation of serial port 4 as an SSP, a summary of serial port 4’s MCP registers, and a summary of its SSP registers.

SA-1100 Developer’s Manual 11-151