Silicon Laboratories SI2494/39 manual Pre-Dial Delay Timer Register, Flash Hook Time Register

AN93

5.7.10. U4E (Pre-Dial Delay Time Register)

U4E sets the delay time between the ATD command carriage return and when the modem goes off-hook and starts dialing (either tone or pulse—see Table 57). This delay establishes the minimum time the modem must be on-hook prior to going off-hook and dialing. France, Sweden, Switzerland, and Japan have minimum on-hook time requirements. The value stored in U4E is the desired delay in milliseconds minus 100 ms. The 100 ms offset is due to a delay inherent in the dialing algorithm. "6.2. Country-Dependent Setup" on page 133 contains information about country-specific values for this register.

5.7.11. U4F (Flash Hook Time Register)

U4F sets the time the modem goes on-hook as a result of a “!” or “&” dial modifier (flash hook). The value is stored in the register in milliseconds (see Table 58).

5.7.12. U50–U51 (Loop Current Debouncing Registers)

U50 (LCDN) sets the loop-current debouncing “on” time, and U51 (LCDF) sets the loop current debouncing “off” time (see Table 59). Loop-current debounce is used in cases where the presence or absence of loop current must be determined prior to taking some action. For example, it may be necessary to verify the presence of loop current prior to dialing. The loop current debounce on-time, LCDN, is used to program a delay in measuring loop current after the modem goes off-hook to ensure the loop current is stable prior to the measurement. LCDN is used in conjunction with U4D [10] (CLPD) and U4D [0] (LCN). Loop current debounce off-time, LCDF, is used in conjunction with LCN to delay the modem going on-hook if loop current is interrupted during a connection. The values are stored in the registers in milliseconds. The default value for LCDN is 350 ms. The default value for LCDF is 200 ms. The range of values for both registers is 0–65535 ms.

5.7.13. U52 (Transmit Level Register)

U52 (XMTL) adjusts the modem transmit level referred to a 600 Ω line (see Table 60). The default value of 0x0000 results in a –9.85 dBm transmit level. U52 can be used to decrease this level in –1 dBm steps approximately to the minimum modem receive threshold of –48 dBm with a register value of 0x0026.

Table 57. Pre-Dial Delay Timer Register

Register	Name	Description	Default
U4E	PRDD	Pre-dial delay-time after ATD command that modem waits to dial (ms	0x0000
		units). The ISOmodem stays on-hook during this time.

Table 58. Flash Hook Time Register

Register	Name		Description	Default
U4F	FHT	Flash hook time (ms units).		0x01F4

Table 59. Loop Current Debounce Registers

Register	Name	Description	Default
U50	LCDN	Loop-current debouncing “on” time (ms units).	0x015E
U51	LCDF	Loop-current debouncing “off” time (ms units).	0x00C8

Table 60. Transmit Level Register

Register	Name	Description	Default
U52	XMTL	Transmit level adjust (–1 dB units).	0x0000

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