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Enhanced Synchronous Serial Interface (ESSI)
7.3 Operation
This section discusses ESSI basics: reset state, initialization, and exceptions.
7.3.1 ESSI After Reset
A hardware
signal or software reset instruction clears the port control register and the port
RESET
direction control register, thus configuring all the ESSI signals as GPIO. The ESSI is in the reset
state while all ESSI signals are programmed as GPIO; it is active only if at least one of the ESSI
I/O signals is programmed as an ESSI signal.
7.3.2 Initialization
To initialize the ESSI, do the following:
1.
Send a reset: hardware
or stop instruction reset.
Program the ESSI control and time slot registers.
2.
3.
Write data to all the enabled transmitters.
Configure at least one signal as ESSI signal.
4.
If an external frame sync is used, from the moment the ESSI is activated, at least five (5)
5.
serial clocks are needed before the first external frame sync is supplied. Otherwise,
improper operation may result.
When the PC[5–0] bits in the GPIO Port Control Register (PCR) are cleared during program
execution, the ESSI stops serial activity and enters the individual reset state. All status bits of the
interface are set to their reset state. The contents of CRA and CRB are not affected. The ESSI
individual reset allows a program to reset each interface separately from the other internal
peripherals. During ESSI individual reset, internal DMA accesses to the data registers of the
ESSI are not valid, and data read there are undefined. To ensure proper operation of the ESSI, use
an ESSI individual reset when you change the ESSI control registers (except for bits TEIE, REIE,
TLIE, RLIE, TIE, RIE, TE2, TE1, TE0, and RE).
Here is an example of how to initialize the ESSI.
1.
Put the ESSI in its individual reset state by clearing the PCR bits.
Configure the control registers (CRA, CRB) to set the operating mode. Disable the
2.
transmitters and receiver by clearing the TE[2–0] and RE bits. Set the interrupt enable
bits for the operating mode chosen.
3.
Enable the ESSI by setting the PCR bits to activate the input/output signals to be used.
Write initial data to the transmitters that are in use during operation. This step is needed
4.
even if DMA services the transmitters.
5.
Enable the transmitters and receiver to be used.
7-6
signal, software reset instruction, ESSI individual reset,
RESET
DSP56311 User's Manual, Rev. 2
Freescale Semiconductor
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