Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 105)

AN93
Rev. 1.3 105
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
 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
units). The ISOmodem stays on-hook during this time. 0x0000
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