Am85C30 - Datasheet Archive

Micro Devices Am85C30 Enhanced Serial Communication Controller Application/Errata Note Am85C30 Enhanced Serial Communication

Advanced Micro Devices Am85C30 Am85C30 Enhanced Serial Communication Controller Application/Errata Note Am85C30 Am85C30 Enhanced Serial Communication Controller (ESCC) Application Note by Shakeel Masood Advanced Micro Devices ESCC or any other device, during the 3 to 3.5 PCLK time period required by the ESCC to complete its internal WRITE, the ESCC may write incorrect data to its internal registers/FIFO. This application note is intended to clarify ESCC operation in relation to the "Valid Access Recovery Time parameter (#49)". PROBLEM ESCC OPERATION The Am85C30 Am85C30 (ESCC) device may have invalid data written into its registers/FIFO if parameter #49 (Trc; Valid Access Recovery Time) is violated. This means that if the system (CPU) does another write operation, to The ESCC WRITE timing with internal state machine WRITE is shown in Figure 1. 49 3.5 PCLKs PCLK WR Next Write Internal WRITE 3 Half PCLKs 30 29 Data Bus D7D0 Valid Data 17315A-1 Figure 1 The ESCC does data writes to its FIFO or registers using an internal WRITE signal synchronized with PCLK. This write signal is generated from a state machine that starts the internal write operation only after the external write (WR) signal goes active and the ESCC synchronizes this high to low transition of WR pulse with PCLK (using the next rising edge of PCLK followed by a falling edge). This synchronization can delay the internal write signal by 1/2 to 1 1/2 clocks depending on the external WR signal relationship to PCLK. The ESCC needs 3-Half (1 1/2) cycles of PCLK to complete the internal write operation. Data is latched internally on the rising edge of the WR signal. The data needs to be valid (setup time; parameter 29-TdWRf[DW]) before the rising edge of the WR and stay valid for the hold time (parameter 30-ThDW[WR]) to this edge for the data to be correctly written to the appropriate register or FIFO. Now if another WR is attempted (to ESCC or to some other device on the same bus) before the internal WRITE is gone inactive (i.e., in violation of parameter #49), this new undesired data could be latched by the WR pulse into the ESCC and subsequently written to its FIFO or registers. Publication# 17315 Rev. A Amendment /0 Issue Date: November 1992 AMD Am85C30 Am85C30 Errata and Workaround Errata 1. Valid Access Recovery Time (Parameter #49) Violation Errata 2. Read Back of Bit 4/ Write Register 5 Problem: Read back of Bit 4 (Send Break)/Write Register 5 does not work, ESCC always returns `1' on read back. ESCC may have invalid data written into its registers/ FIFO if another WRITE (to ESCC or some other device with the common WR strobe) is attempted during the valid access recovery time (i.e., parameter #49). The ESCC does not qualify the write strobe (WR) with chip enable (CE). In most applications PCLK is same or faster than CPU clock and the CPU cannot do another read or write access in the recovery time required by the ESCC, thus the above will not be a problem. Problem: Workaround: None. Workaround: If PCLK is slower than CPU clock, then any extra nonESCC WRITEs during the valid access recovery time can be stopped by gating the external WR with CE of the ESCC (see Figure 2 below). CE CE WR WR Am85C30 Am85C30 ESCC 17315A-2 Figure 2 As far as extra ESCC WRITEs during the same valid access recovery time, there cannot be a workaround as this is a violation of parameter #49. 2 Am85C30 Am85C30 (ESCC)