Essi Initialization; Operating Modes - Motorola DSP56305 User Manual

24-bit digital signal processor
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Enhanced Synchronous Serial Interface (ESSI)

Operating Modes

When the RSMA or RSMB register are read by the internal data bus, the register contents
occupy the two low-order bytes of the data bus, and the high-order byte is zero-filled.
After a hardware reset or a software reset instruction, the RSM register is reset to
$FFFFFFFF. This enables all thirty-two time slots for data reception.
7.5
OPERATING MODES
The ESSI operating modes are selected by the ESSI Control Registers (CRA and CRB).
The operating modes are described in the following paragraphs.
7.5.1

ESSI Initialization

A hardware reset signal or software reset instruction clears the Port Control Register and
the Port Direction Control Register. This configures all the ESSI signal signals as GPIO.
The ESSI is in the reset state while all ESSI signals are programmed as GPIO and is active
only if at least one of the ESSI I/O signals is programmed as an ESSI signal.
To initialize the ESSI do the following:
1. Send a reset: hardware, software, ESSI individual, or STOP instruction reset.
2. Program the ESSI control and time slot registers.
3. Write data to all the enabled transmitters.
4. Configure at least one signal as ESSI signal.
5. If an external frame sync will be used, from the moment the ESSI is activated, at
least five (5) serial clocks are needed before the first external frame sync is
supplied. Otherwise, improper operation may result.
Clearing the PC[5:0] bits in the GPIO Port Control Register (PCR) during program
execution causes the ESSI to stop serial activity and enter the individual reset state. All
status bits of the interface are set to their reset state, but 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 is undefined.
To ensure proper operation of the ESSI, use an ESSI individual reset when changing the
ESSI Control Registers (except for bits TEIE, REIE, TLIE, RLIE, TIE, RIE, TE2, TE1, TE0,
and RE).
7-42
DSP56305 User's Manual
MOTOROLA

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