Datasheet

DS21Q59 Quad E1 Transceiver
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15. TRANSMIT CLOCK SOURCE
Depending on the DS21Q59’s operating mode, the transmit clock can be derived from different sources. In a basic
configuration, where the IBO function is disabled, the transmit clock is normally sourced from the TCLK pin. In this
mode, a 2.048MHz clock with ±50ppm accuracy is applied to the TCLK pin. If the signal at TCLK is lost, the
DS21Q59 automatically switches to either the system reference clock present on the REFCLK pin or to the
recovered clock off the same port, depending on which source the host assigned as the backup clock. At the same
time the host can be notified of the loss-of-transmit clock through an interrupt. The host can at any time force a
switchover to one of the two backup clock sources regardless of the state of the TCLK pin.
When the IBO function is enabled, the transmit clock must be synchronous to the system clock since slips are not
allowed in the transmit direction. In this mode, the TCLK pin is ignored, and a transmit clock is automatically
provided by the IBO circuit by dividing the clock present on the SYSCLK pin by 2, 4, or 8. In this configuration, if the
signal present on the SYSCLK pin is lost, the DS21Q59 automatically switches to either the system reference clock
or to the recovered clock off the same port, depending on which source the host assigned as the backup clock. The
host can at any time force a switchover to one of the two backup clock sources regardless of the state of the
SYSCLK pin.
16. IDLE CODE INSERTION
The transmit idle registers (TIR1/2/3/4) determine which of the 32 E1 channels should be overwritten with the code
placed in the transmit idle definition register (TIDR). This allows the same 8-bit code to be placed into any of the 32
E1 channels. Each of the bit positions in the transmit idle registers represents a DS0 channel in the outgoing frame.
When these bits are set to 1, the corresponding channel transmits the idle code contained in the TIDR.
Register Name:
TIR1, TIR2, TIR3, TIR4
Register Description:
Transmit Idle Registers
Register Address:
24 Hex, 25 Hex, 26 Hex, 27 Hex
Bit # 7 6 5 4 3 2 1 0
CH8 CH7 CH6 CH5 CH4 CH3 CH2 CH1
CH16 CH15 CH14 CH13 CH12 CH11 CH10 CH9
CH24 CH23 CH22 CH21 CH20 CH19 CH18 CH17
Name
CH32 CH31 CH30 CH29 CH28 CH27 CH26 CH25
NAME BIT FUNCTION
CH1 to CH32 TIR1.0 to 4.7
Transmit Idle Code-Insertion Control Bits
0 = do not insert the idle code in the TIDR into this channel
1 = insert the idle code in the TIDR into this channel
Register Name:
TIDR
Register Description:
Transmit Idle Definition Register
Register Address:
23 Hex
Bit # 7 6 5 4 3 2 1 0
Name TIDR7 TIDR6 TIDR5 TIDR4 TIDR3 TIDR2 TIDR1 TIDR0
NAME BIT FUNCTION
TIDR7 7
MSB of the Idle Code (This bit is transmitted first.)
TIDR6 6 —
TIDR5 5 —
TIDR4 4 —
TIDR3 3 —
TIDR2 2 —
TIDR1 1 —
TIDR0 0
LSB of the Idle Code (This bit is transmitted last.)