L9963E datasheet(160/184 Pages) STMICROELECTRONICS

160 / 184 page

Minimum Inter-Frame Delay Estimation

TINTER_FRAMEmin=2×NDEVICES× TWIREDELAY+TINSERTIONDELAY +41TBITLENGTH+TANSWER_DELAY

TWIRE_DELAY=3.335× εr×LWIRE ns

TINSERTIONDELAY=TBIT_LENGTH

TBITLENGTH=TBITLENGHTFAST or TBITLENGHTSLOW

TANSWER_DELAY= TANSWER_DELAY_FAST or TANSWER_DELAY_SLOW

(20)

Where εr is the relative permittivity of the dielectric material of the twisted pair, and TBIT_LENGTH depends on

the iso_freq_sel bit. The insertion of a L9963E introduces less than a bit time delay. Each L9963E acts as a

buffer, regenerating the signal. Hence, attenuation should not represent an issue.

For instance, a daisy chain of 14 devices with 2 m long wires between each node, with a twisted pair made of

copper conductor and polyethylene insulator (εr = 2.25), requires a 38.25 μs inter-frame delay when operating in

high frequency mode, and a 282 μs delay when in low speed configuration.

ST recommends using at least 1.5 times the minimum inter-frame delay estimated. This compensates the

formula inaccuracy and all the external factors that could influence transmission delay. For instance, in the

example above, the recommended inter-frame delay would be 425 μs for low frequency operation and 60 μs for

the high speed configuration.

Since the protocol is out of frame, when switching from a frequency mode to another, the following frame must still

be issued after the old inter-frame delay.

6.11.6

Choosing the twisted pair

L9963E vertical communication interface has been extensively validated at bench using a 24 AWG, 10 m long,

unshielded twisted pair, whose insulating material is a 100 V rated PVC, with a relative permittivity εr = 4.

Different wires can be used, taking into account the following recommendations:

•

Changing the wire AWG and/or length may affect signal attenuation. If signal appears too attenuated at

receiver side, the transmitter amplitude can be increased acting on out_res_tx_iso

•

Increasing the wire length will lead to higher signal propagation delays, eventually degenerating in inter-

symbolic interference. Propagation delay can be estimated using the following equation

Signal propagation delay estimation on vertical communication interface

TPDns/m =3.335 εr

(21)

Figure 54 plots the signal propagation delay (ns) vs. different wire insulating materials. Referring to Figure 10, if

such a delay exceeds 2TPULSE, the transmitter starts generating a new symbol before the receiver has finished

receiving the previous one. The wire becomes acting as a transmission line and intersymbolic interference may

occur.

The worst case is represented by operation at high-frequency (FISO_FAST), determining a constraint of 250 ns

max. propagation delay. On the contrary, switching to low frequency (FISO_SLOW) allows reaching longer distances

(paying always attention to signal attenuation, that must be verified on receiver side).

L9963E

Communication architectures

DS13636 - Rev 12

page 160/184

L9963E 数据表(PDF) 160 Page - STMicroelectronics

L9963E 数据表(HTML) 160 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载